Opinion by
Mr. Chief Justice Moschzisker,This is an appeal from a decree dismissing a bill in equity; plaintiffs, man and wife, asked that defendant, a *494Pennsylvania corporation, be restrained from mining any coal underlying the former’s property in tbe City of Pittston, “tbe removal of which will cause the caving-in, collapse or subsidence of their dwelling house,” contrary to the Act of May 27, 1921, P. L. 1198, commonly known as the Kohler Act.
At the outset, it may be stated that, so far as the contractual rights of the respective parties are concerned, as shown by the paper title to the properties involved, defendant is expressly authorized to mine the subjacent strata owned by it without any obligation to support the surface owned by plaintiffs.
The court below found that, “if not restrained, defendant .....will.....cause the caving-in, collapse and subsidence of the surface, together with the dwelling, entailing injury upon plaintiffs”; but refused an injunction, on the ground that “the owner of the coal has an absolute right to remove the whole of the same, free from all liability for injury thereby inflicted,” and “no interest is involved......except the private interests of the plaintiffs in the prevention of a private injury.”
The position assumed by the learned court below raises, as the sole question for consideration, the applicability of the Kohler Act to the facts of this particular case; but the discussion of counsel, representing the parties to the cause and those who were allowed to intervene at argument, including the city solicitor and the attorney general of the State, has taken a much wider range, and calls for consideration, first of all, of the constitutionality of the act itself, as a reasonable and valid exercise of the police power.
The statute is entitled: “An act regulating the mining of anthracite coal; prescribing duties for certain municipal officers; and imposing penalties.” This title is sufficient to cover the contents of the enactment.
Section 1 provides that it shall be unlawful “so to conduct the operation .of mining anthracite coal as to cause *495the caving-in, collapse, or subsidence of (a) Any public building or any structure customarily used by the public as a place of resort, assemblage, or amusement, including, but not being limited to, churches, schools, hospitals, theatres, hotels, and railroad stations; (b) Any street, road, bridge, or other public passageway, dedicated to public use or habitually used by the public; (c) Any track, roadbed, right-of-way, pipe, conduit, wire, or other facility, used in the service of the public by any municipal corporation or public service company as defined by the Public Service Company Law; (d) Any dwelling or other structure used as a human habitation, or any factory, store, or other industrial or mercantile establishment in which human labor is employed; (e) Any cemetery or public burial ground.”
Sections 2 to 5, inclusive, place certain duties on public officials and persons in charge of mining operations, to facilitate carrying out the purposes of the act.
Section 6 provides the act “shall not apply to [mines in] townships of the second class [i. e., townships having a population of less than 300 persons to a square mile], nor shall it apply to any area wherein the surface overlying the mine or mining operation is wild or unseated land, nor where, such surface is owned by the owner or operator of the underlying coal and is distant more than one hundred and fifty feet from any improved property belonging to any other person.”
Section 7 sets forth penalties; and section 8 reads: “The courts of common pleas shall have power to award injunctions to restrain violations of this act.”
The remaining sections state: when the statute takes effect; that inconsistent legislation is repealed; that “This act is intended as remedial legislation, designed to cure existing evils and abuses, and each and every provision is intended to receive a liberal construction such as will best effectuate that purpose”; and that all provisions “are severable one from another.”
*496In determining whether the act is reasonable legislation within the police power, we may “call to our aid all those external or historical facts which are necessary for this purpose and which led to the enactment” : Endlich, Interp. of Stats., s. 29.'
The anthracite coal field of Pennsylvania comprises a large area, on the surface of which have grown up, and now exist, many cities, boroughs and villages, containing a population of approximately a million persons. When this district was sparsely peopled, the caving-in of the surface was not of public moment; but, within the past fifteen or twenty years, it has become a matter of widespread notoriety that these disturbances menace the safety and material welfare of the inhabitants of communities in that part of the State. During the period mentioned, the facts have been put before the public, not only by news of the collapse of streets and the fall of buildings, but also through the reports of commissions created by joint resolutions of the legislature and by means of numerous proposed statutes, antedating the present law, introduced into that body, some of which passed and others did not; likewise, by messages from the governor of the Commonwealth addressed to the general assembly.
The conditions that gave rise to the act are summarized in a preamble thus: “Whereas, the anthracite coal industry in this. Commonwealth has been and is being carried on in populous communities in such a manner as to remove the entire support of the surface of the soil to such an extent as to result in wrecked and dangerous streets and highways,, collapsed public buildings, churches, schools, factories,' streets, and private dwellings, broken gas, water and sewer systems, the loss of human life, and in general so as to threaten and seriously endanger the lives and safety of large numbers of the people of the Commonwealth; therefore be it enacted,” etc.
*497In signing the bill, the governor stated of record that “lives have been lost, homes, churches and schools destroyed, and an ever-present peril has threatened the morale of the entire community”; adding, “for a generation, the appeal..... .to save the situation has been heard at the capital.”
It is not denied on the present record' that the conditions above described exist; and the legislature having. declared in terms what, in a general way, had become a; matter of public notoriety, we must accept such declaration as a correct statement of facts: People ex rel. Durham Realty Corp. v. La Fetra, 230 N. Y. 429, 440; Lower Vein Coal Co. v. Industrial Bd., 255 U. S. 144, 148; Block v. Hirsh, 256 U. S. 135, 154; Marcus Brown Holding Co. v. Feldman, 256 U. S. 170, 198.
That the conditions portrayed in the legislative declaration are such as to create an emergency, properly warranting the exercise of the police power, is sufficiently obvious not to call for extended discussion. It is primarily for the legislature to consider and decide on the fact of a danger, then meet it by a proper remedy: Stafford v. Wallace, 42 U. S. Supreme Ct. Rep. (issue of June 9,1922), 397, 401.
Of course, the cure must always bear a substantial relation to the existing evil, and must not constitute a mere attack on property rights, disguised as an exercise of the police power. In judging of this, however, it is to be remembered that “in order to serve the public welfare, the State, under its police power, may lawfully impose such restrictions upon private rights as, in the wisdom of the legislature, may be deemed expedient; for all property in this country is held under the implied obligation that the owner’s use of it shall not be injurious to the community......[and] a statute enacted for the protection of public health, safety or morals can be set aside by the courts only when it plainly has no real or substantial relation to these subjects or is a *498palpable invasion of rights secured by the fundamental law; if it does not appear upon the face of the statute, or from any facts of which the court must take judicial cognizance, that it infringes rights secured by the fundamental law, the legislative determination is conclusive”: Nolan v. Jones, 263 Pa. 124, 127-8, and authorities there cited.
It has often been decided of recent years that the mere fact of an exercise of the police power interfering with the use of property will not render such exercise unconstitutional. A host of authorities on this point might be cited, but it is not necessary to go beyond our own recent cases. In Nolan v. Jones, supra, at page 131, discussing another case (Com. v. Charity Hospital, 198 Pa. 270, 277) that dealt with an act which prevented a hospital from erecting additional buildings on real estate owned by it, we said that such deprivation was not a violation of the Fourteenth Amendment, and did not take from the complainant its property without due process of law, adding, “It is true the act does prevent the [hospital] from using its property in a manner which before was lawful, but [since]......the act in question is......a valid police regulation......defendant has no cause of complaint.” This last mentioned principle applies here, for the statute before us is a police measure which does not, in any true legal sense, contemplate the taking of private property for public use (Com. v. Plymouth Coal Co., 232 Pa. 141, 149), or the transferring of it from one person to another: Jackman v. Rosenbaum Co., 263 Pa.' 158, 167-70, and authorities there cited. In fact, the prayers of the present bill suggest no such intention; they are, first, as quoted at the head of this opinion; second, that defendant be restrained from “so conducting its mining operations as to cause the caving-in, collapse or subsidence of plaintiff’s dwelling”; and, third, for general relief — in other words, for such incidental interference with defendant’s property rights, and such only, *499as may be necessary in order to carry out the declared public policy of the State.
Incidental interference with property rights, by legislation regulating the mining of coal, is by no means new to Pennsylvania; such interferences have invariably been upheld as proper exercise of the police power: see Com. v. Plymouth Coal Co., 232 Pa. 141, and cases there cited, affirmed by the Federal Supreme Court in Plymouth Coal Co. v. Pennsylvania, 232 U. S. 531.
True, in Com. v. Clearview Coal Co., 256 Pa. 328, I 330-1, we ruled, on the law as it then stood, that a defendant, possessed of the contractual right to let down the surface, would not be “restrained from mining coal under a school building, to the injury thereof,” at the suit of one who held title to the surface subject to that right, saying, inter alia, “it is difficult to understand how the doing of a lawful act in a lawful manner can constitute such a public nuisance as will be restrained in equity”; but “circumstances may so change in time ......as to clothe with [a public] interest what at other times......would be a matter of purely private concern” (Block v. Hirsh, 256 U. S. 135, 155), and, since the date of the Clearfield decision, the Kohler Act has been passed, declaring, in effect, mining such as threatened by the present defendant to be a public nuisance. ¿J,
It always has been the law of Pennsylvania that the surface owner was entitled to support unless he released or waived his right, but when he did so, he would be held to his contract; the law, as thus developed, was pronounced and acted upon in the Clearfield case. After that pronouncement, however, the general assembly,— taking cognizance of the change in conditions wrought by time and new methods of mining, and of the increasing public harm worked by the rule theretofore adhered to, — altered the law in so far as it applied to certain presumably thickly populated areas in the hard-coal district, forbidding such mining operations as would cause the letting down of the surface under, inter alia, “any *500dwelling or other structure used as a human habitation,” aaid providing for restraint by injunction. Thus the law in the Clearfield case, so far as it might apply to the facts at bar, is effectually overruled by those who have the right to declare the public policy of the State; and this legislative pronouncement, as also the means provided to carry it into effect, is binding on us, unless a palpable abuse of power appears, or unless it can be demonstrated that the statutory relief thus provided is plainly forbidden by the organic law.
We said, in Pennsylvania E. E. Co. v. Ewing, 241 Pa. 581, 589, “The scope of judicial inquiry in deciding questions of power is not to be confused with the scope of legislative considerations in dealing with matters of policy; whether an enactment is wise or not, whether it is based on sound economic theory, whether it is the best means to achieve the desired result, whether, in short, the legislative discretion within its prescribed limits should be exercised in a particular manner, are matters for the judgment of the legislature, and the earnest conflict of serious opinion does not suffice to bring them within the range of judicial cognizance,” citing Chicago, etc., R. R. Co. v. McGuire, 219 U. S. 549.
The Federal Supreme Court, dealing with the general subject in hand, said in Lawton v. Steele, 152 U. S. 133, 140: “While the legislature has no right arbitrarily to declare that to be a nuisance which is clearly not so, a good deal must be left to its discretion in this regard, and, if the object to be accomplished is conducive to the public interests, it may exercise a large liberty of choice in the means employed”; see also Shelby v. Cleveland Power Co., 155 N. C. 196, 201; Village of Atwood v. Otter, 296 Ill. 70, 81, 129 N. E. 573, 577.
In view of the facts which gave rise to the act now before us, we cannot say the questions involved were not for legislative decision; nor can it be held, under the authorities, that the contractual right of defendant to let down the surface is rendered dominant by the various *501constitutional provisions depended on by appellee (Bowman v. Chicago Ry. Co., 125 U. S. 465, 517; Chicago, etc., R. R. Co. v. McGuire, 219 U. S. 549, 569; McLean v. Arkansas, 211 U. S. 539, 547; Atlantic C. L. R. R. Co. v. Goldsboro, 232 U. S. 548, 558; Levy Leasing Co. v. Siegel, 42 Supreme Ct. R. 289, 292, issue of April 15, 1922, and cases there cited); particularly is this so when we consider the mandate of our Constitution (article XYI, section 3) that “the exercise of the police power of the State shall never be abridged or so construed as to permit corporations to conduct their business in such manner as to infringe the......general well-being of the State”: Scranton v. P. S. C., 268 Pa. 192, 195.
The police power, “legitimately exercised, can never be limited by contract nor bartered away by the legislature” (Holden v. Hardy, 169 U. S. 386, 392; see also N. Pacific Ry. Co. v. Minn, 208 U. S. 583, 596, 597); and this court, in dealing with the police power has repeatedly held that private contracts cannot interfere with its legitimate exercise by the State; the theory being that all contracts raising rights or imposing obligations, the exercise of which may affect the public welfare, are, of necessity, made subject to the reserved right of the State to modify them by legitimate assertion of the police power: Leiper v. B. & P. R. R. Co., 262 Pa. 328, 332; Scranton v. P. S. C., 268 Pa. 192, 197-8.
It was the harmful results, to the community as a whole, of contracts granting the right to let down the surface under any and all circumstances, that gave rise to the statute now attacked; and the power to enforce the public policy of the State, declared in this legislation, cannot be defeated because those who move the court (plaintiffs at bar) are parties to such a contract.
The legal right of these individual plaintiffs to proceed in equity is not questioned in the pleadings, and no one, directly or indirectly involved in the present suit, raises any point against such right; but, since it is a *502matter of public importance, the court itself asked that printed arguments be submitted thereon. After reading the various briefs prepared by learned counsel, we are convinced there is nothing in the law to prevent plaintiffs from prosecuting these proceedings; as we shall now show.
First, since the statute itself contains a provision for its enforcement by injunction, the fact that violations thereof constitute a misdemeanor, is of no moment. Next, we have already held, supra, that the fact of plaintiffs’ contract, granting defendant a right to let down the surface of the land in question, cannot interfere with the enforcement of the declared public policy of the State; hence appellants’ peculiar special interest, — affected, as it is, by a waiver of surface support which antedates the legislative declaration of public policy, — constitutes no bar against their coming within the general rule that persons with a special interest may have public nuisances abated at their own suit: as to the right of persons with a special interest to such relief, see Klein v. Livingston Club, 177 Pa. 224, and cases there cited; and, for relevant authorities from other jurisdictions, see Kaufman v. Stein, 138 Ind. 49; People’s Gas Co. v. Tyner, 131 Ind. 277; Cranford v. Tyrrell, 128 N. Y. 341; Joos v. Illinois Nat. Guard, 257 Ill. 138; also a statement of the general rule in 20 R. C. L. 476, s. 90. It is not necessary to depend upon plaintiff’s special interest, however, for, under the Kohler Act, they may be viewed as moving the court to enforce a general rule of public policy, intended for the protection of the whole community, rather than as acting simply for their own protection. As said in Com. v. Plymouth Coal Co., 232 Pa. 141, 146, quoting from and citing other authorities: “The whole is no greater than the sum of all its parts, and when individual......safety and welfare are sacrificed, the State must suffer.” Every habitation thrown to the ground in the course of the operations of a vast industry, — the manner of conducting which has caused many such oc*503eurrences, — with the dangers to human life and other direful possibilities that attend these happenings, can well be considered as part of a general harm, against which the legislature, exercising the police power of the State, may properly provide. Finally, the authorities indicate that it is competent for the legislature to vest a civil remedy in any citizen, irrespective of his special interest, to enforce a declaration of public policy, and this the present act does in effect. The principle involved is thus stated in Littleton v. Fritz, 65 Iowa 488, 496: “There can be no doubt it is within the power of the legislature to designate the person or class of persons who may maintain actions to restrain a public nuisance, and, when that is done, the action is, for all purposes, an action instituted in behalf of the public, the same as though brought by the attorney general or public prosecutor.” In this connection, our own case of Craig v. Kline, 65 Pa. 399, 410, 412, shows the State may authorize its citizens, individually, to assist in the enforcement of police regulations, albeit no property interest of the particular plaintiff has been specially affected by the violation complained of. Though plaintiffs’ right to institute the present suit cannot be opposed successfully, yet the act of assembly itself is attacked on other grounds, which call for consideration.
Appellee stigmatizes the act as local and special legislation, forbidden by the Constitution. The facts that the statute is inapplicable to bituminous coal mines, to operations located in townships having a populátion of less than 300 to the square mile, and to “any area wherein the surface overlying the......operation is wild or unseated land,” or “where such surface is owned by the owner or operator of underlying coal and is distant more than 150 feet from any improved property belonging to any other person,” do not, on the grounds of local or special legislation, constitute it a violation of the organic law of Pennsylvania; proper classification is permissible, and the act before us is in that category.
*504Laws enacted in pursuance of a necessity that springs from manifest peculiarities, distinguishing the persons, objects or localities legislated for, from other classes as to which the legislation in question would be useless and detrimental, are, properly speaking, neither local nor special, — they are general, because governing all persons, objects or localities similarly situated (Ayars’s App., 122 Pa. 266, 281; Com. v. Gilligan, 195 Pa. 504, 510); such grouping is permissible and cannot be set aside by the court's for that reason.
“Classification is a legislative question, subject to judicial revision only so far as to see that it is founded on real distinctions in the subjects classified”: Seabolt v. Commissioners, 187 Pa. 318, 323. Here the distinctions are real and fully warrant the classifications in hand.
To begin with, the fact that the present act distinguishes coal mining from other sorts of mining cannot prevail against the validity of the statute in the absence of some warrant for holding the resulting classification to be without reason; for, nothing appearing to the contrary, it is “assumed the legislature proceeded after full examination” and made the distinction on proper grounds: Nolan v. Jones, 263 Pa. 124, 128, and cases there cited. Next, the distinction between mining operations in the anthracite and in the bituminous coal fields has been constantly and consistently recognized in our law, both by the courts and the legislature, for many years, and is now well established: see Act March 3, 1870, P. L. 3, construed in Williams v. Bonnell, 8 Phila. 534; Act June 2, 1891, P. L. 176, construed in Durkin v. Kingston Coal Co., 171 Pa. 193; Act May 15, 1893, P. L. 52, construed in Com. v. Jones, 4 Pa. Superior Ct. 362; see also Com. v. Grossman, 248 Pa. 11, 18; Com. v. Alden Coal Co., 251 Pa. 134, 139. Lastly, the other distinctions, before mentioned, are all founded on differences arising from the fact of density, or lack of density, of population; and such circumstances have repeatedly *505been considered as constituting a sound basis of classification.
In connection with the statement just made, — that conditions of population form a proper ground of classification, — see, for example, Com. v. Charity Hospital, 198 Pa. 270, 276-7, 283, where an act prohibiting the “establishing or maintaining of additional hospitals, pest houses or burial grounds, in built-up portions of cities,” was attacked as local or special legislation. In sustaining the act, the court below said: “There is obviously much greater danger to the general public health from [hospitals, etc.] in a populous city than in the country, or in a village, and the danger will be in proportion to the number and density of the population......; when, therefore, a statute prohibits hospitals, etc., in the built-up portions of cities it thereby draws a line, having the populous centers on one side and the less populous on the other, in a case where the supposed evil does or does not exist, according to the greater or less density of population.” We adopted this reasoning, per curiam. The Anthracite Mining Act of June 2, 1891, P. L. 176, applies solely to mines of that character, located in certain parts of designated counties, employing a working force of “more than ten persons” ; it was sustained in Durkin v. Kingston Coal Co., 171 Pa. 193, 204. Again, party wall legislation is applicable to “congested districts” alone: Jackman v. Rosenbaum, 263 Pa. 158, 173. On the general subject of classification according to population, Wheeler v. Phila., 77 Pa. 338, and Beltz v. Pittsburgh, 26 Pa. Superior Ct. 66, may be cited.
The act before us expressly recognizes the evident fact that conditions attendant upon mining operations in densely populated communities differ greatly from, and, so far as surface support goes, are more dangerous than those in sparsely settled or uninhabited districts; this difference warrants the classification here involved: Com. v. Hanley, 15 Pa. Superior Ct. 271; Beltz v. Pitts*506burgh, 26 Pa. Superior Ct. 66. Had the distinction based upon density of population not been adopted, and had the legislation been made to apply to mines in sparsely settled townships, then, since every exercise of the police power must be reasonable, appellees might, perhaps, have argued with some force that it was useless and detrimental to carry out the provisions of the statute in localities where both common sense and common consent would declare no necessity or danger existed; thus the argument against the classification adopted seems to defeat itself.
In Ruan Street, 132 Pa. 257, 276, this court said: “Among the many subjects of legislation which classification presents [are]......the preservation of the public health, protection against fire,” etc.;, and to this statement, of course, may be added, “the preservation of the public safety.” The whole structure of the present act manifestly rests on that basis, and its justification is reinforced by the previously quoted preamble.
While on the subject of the preamble, it may be well to note that, although this part of the bill does not appear at the head of the statute in the published volume of laws for the year in question, the legislative records show it was passed and then eliminated in the printing of the law, under the Act of June 3, 1911, P. L. 664, which, very unwisely, we think, directs that “No preamble......shall be printed when such bill becomes a law and is printed for general use.”
The objection that sections 4 and 5 of the act offend against the provision of our Constitution which forbids local or special legislation “prescribing the powers and duties of officers in cities, boroughs and townships,” need not be considered, since no question arising thereunder is properly before us.
Upwards of 200 authorities have been submitted for our consideration. We have studied all with which we were not already familiar, and cited a number which seem relevant, some with discussion; other, omitted, may *507be as appropriate as those mentioned, but'a proper regard for the length of this opinion forbids their use. Of course, many of the authorities noted comprehend rulings on a state of facts essentially different from those now before us; but, in such instances, the opinions will be found to contain either illustrative discussions or statements of appropriate general principles, and the cases are used for that reason, not necessarily in approval of rulings they may happen to include. Finally, we need not discuss further the authorities depended on by appellee; it is sufficient to say that none of them controls the present case.
The order appealed from is reversed and the bill reinstated; the record is remitted, and the court below is directed to enter a decree in accord with the views expressed in this opinion; appellee to pay the costs.