1. The trees upon the plaintiffs’ land having been prostrated by a gale, the defendant entered upon the premises, trimmed the trees, and cut some of them into short logs, called box-board logs. All the timber remained upon the land, and enured to the benefit of the owners of the land, free from any claim for the cutting which had been done by the defendant. It is impossible to ascertain the injury done to the plaintiffs by the acts of the defendant, except by comparing the value of the timber as it lay when prostrated, with its value after the defendant had trimmed and cut it into box-board logs. If the value of the box-board logs was greater than, or as great as, the value of the timber before the defendant interfered with it, the plaintiffs *241sustained no injury. If it was less, the injury of the plaintiffs is measured by the difference between the two values. No witness therefore was competent to give an opinion upon the question of the effect of the acts of the defendant upon the value of the timber, unless he had knowledge both of the value of the timber before and of its value after it was cut into box-board logs. The witnesses offered by the plaintiffs had sufficient knowledge to render them competent to give an opinion as to the value of the timber before it was cut into logs; but they had no knowledge of the market value of box-board logs. As the answer to the question put to them involved a knowledge of the value of such logs, to make it competent, the question was rightly ruled out by the court. »
2. The exception to the ruling of the court, permitting the defendant to testify to his opinion as to the value of box-board logs, cannot be maintained. He had been for many years engaged in sawing and buying and selling such logs, in neighboring towns, and had erected a mill for sawing them in the immediate vicinity of the premises. He is thus shown to possess unusual knowledge upon the subject as to which his opinion was asked. On the question of the sufficiency of the knowledge of the witness, much must be left to the discretion of the presiding judge; and if we can revise his ruling in this case, we are of opinion that it was correct. Swan v. Middlesex, 101 Mass. 173.
3. Upon the question of the value of the timber in controversy before it was cut by the defendant, the plaintiffs offered to show the price which another lot of timber, on a lot across the highway, and which had been prostrated by the same gale, brought at an auction sale. The admissibility of this testimony depended upon the question whether the two lots of timber were so far similar as to afford a comparison which would enable the jury to ascertain the value of the timber in question. This question must be passed upon by the presiding judge in the first instance; and the exercise of his discretion in rejecting or admitting the evidence will not be revised by this court, unless all the facts upon which his decision was founded are reported. Presbrey v. Old Colony & Newport Railway Co. 103 Mass. 1. Shattuck v. Stone*242ham Branch Railroad Co. 6 Allen, 115. This bill of exceptions does not show all the facts upon which the ruling excepted to was founded. It does not show that the two lots of timber were in similar condition. The effect of the gale upon the two lots may have been very dissimilar, and the condition of the timber may have been so far different that the value of one wotild afford no safe criterion of the value of the other. The bill of exceptions does not show that the decision of the judge upon this question was erroneous. Standish v. Washburn, 21 Pick. 237.
Exceptions overruled.