delivered the opinion of the court,

The principles, as well as the main facts of this case, are few and simple. The whole body of coal mentioned in the leases with Freck & Blackiston, and with Gorrell & Co., the former dated August 18th 1862, the latter January 11th 1868, belonged to the Locust Mountain Coal and Iron Company. The general vein or stratum, thus leased, lay in the Centraba or Centreville basin, and a cross section of it, in shape, resembles very much the letter Y, *325except that the vein is rounded at the bottom. The northern part, called the “south dip,” was that leased to Freck & Blackiston; the southern side, or “north dip,” to Gorrell & Co. It follows, that the line, dividing these two leases, was the middle line of this basin, or that from which the two sides begin to ascend, called, technically, the synclinal axis. Either or both these parties had the right, under their respective leases, to take out all the coal down to this line. The coal company was the common lessor of both parties, and, hence, the rules governing adjacent mines when owned by different owners, cannot apply to the company plaintiff, for having the power so to do, if it neglected to protect itself by covenant, it cannot plead rules, resulting ex necessitate rei, as against its own grant. It follows that if both parties, in strict accordance with the terms of their several leases', had worked down to the synclinal axis, they would have brought the two mines together, and so produced ' every result now complained of, except such as may have arisen from the criminal negligence of one or both of the lessees. The company, therefore, has no right to complain of the mere conjunction of these workings, for this is but the result of its own grant; and it follows, that unless it can show some wrong done in the manner in which Freck conducted his workings, it has no standing to maintain this suit. Now as there is no question as to the character of Freck’s work, so far as his own lease extended, our inquiry must be limited to a single point, to wit: was the damage complained of the result of Freck’s wilful trespass upon the adjacent lease ? His southern boundary, the synclinal axis, could, by no human possibility, be ascertained until developed by the proper w-orkings. Yet Freck had the right, under his lease, to go to that line, and this necessarily involved the further right of ascertaining this line, by the best means in his power. It is here that the court below committed an error, in treating the case as one between distinct landowners; in such case the doctrine that the lessee must ascertain the dividing line at his peril, would-be correct, and though he passed over it with the best possible intentions, he would nevertheless bé a trespasser. Not so, when the lessor, not only gives his tenant the power, but makes it his duty, to explore and mark a theoretical line upon his own premises. In such case the tenant cannot be treated as a trespasser if, in an honest attempt to ascertain that line, he should chance to pass over it; for the right to do what is necessary in order to find and fix that line is implied in the grant by which it is made a boundary. Freck had a right to ascertain his southern line, and if he did no more than was necessary for this purpose he was not a trespasser. The difficulties, in the accomplishment of this result, become apparent by a glance at the map before us, on which we observe the plottings for the synclinal axis in no less than five different places. It is thus apparent that the true line, the one finally adopted, was only conclusively set-*326tied after Ereck’s workings had enabled the engineers to ascertain its true location.

But there was not a day, not an hour, during the progress of this work, when this company had not the power to put an end to these operations, on the discovery that the lessee was working beyond the bounds of his lease.

In that lease it had retained full supervisory powers ; the work was done under the constant inspection of its own engineer, and in case of dispute it had the power to settle all matters by arbitration. And if, under such circumstances, being fully and accurately informed of Ereck’s operations, it chose to stand by and permit him to prosecute his researches, according to the best of his judgment, at the same time receiving the products of his labor as so much rent under the lease, by what rule of justice can it now treat him as a trespasser ? If we examine the notice of Mr. Stockett, the plaintiff’s engineer, dated April 21st 1871, when Ereck’s gangway had already been driven south of what afterwards proved to be the true synclinal axis, we find two things worthy of observation. 1. He is notified not that his gangway, but “ a part of the breasts turned on the south side of your east gangway of the second lift on the Mammoth Yein, is beyond the limits of your lease.” 2. That “ the object of the notice is to prevent any infringement on the rights granted to 'the lessees.” Thus we observe that, even as yet, the true position of the dividing line was not discovered, and that the defendant’s workings were not regarded as likely to prove injurious to the rights of the company, and he was warned only to avoid interference with the lease of the adjoining tenants. Then we have Mr. Stockett’s letter of the same date to the president of the company, detailing the conversation he had had with Freck and his mining-boss, Williams; the confidence they expressed that there was yet another south dip between the breasts referred to, and the adjacent lease of Gorreil & Co., and his own opinion that whilst this was possible it>was not probable. Thus the company, by its own officer, was put into possession of every detail, not only of Ereck’s doings, but of his intentions and opinions, and if it trusted him, without remonstrance or caution, to proceed with his experiments in good faith, we cannot see why it should complain of the result.

Again, the defendant ought not to be held liable for damage resulting from the neglect of either the plaintiff or Gorreil & Co. It is manifest, from the facts of this case, as well as of the case of this same plaintiff against the last-named compaliy, as reported in the Leg. Int. of 29th March 1872, that much, if not all, of the damage to the Centraba mines resulted from the intentional acts of the lessees of Hazeldell, in so sloping their gangway as to throw the water into the Ereclc workings. But the plaintiff had the same powers over Gorreil & Co. that it had over Freck & Blackiston, *327and if it passively permitted the former to do that which proved disastrous to its own property, it cannot cast the burden of its own negligence over .upon the defendant. We see,-from the case above stated, that when it chose to move, there was no want of powers, and that it could then make itself felt to some purpose, not only through the reserved powers of the lease, but also through the strong arm of this court.

Without dwelling upon any of the numerous exceptions, we but suggest, by way of summary, the following principles for the re-trial of this case.

If the crossing of the line of the two leases, by Freck, resulted from an error in judgment in an honest- attempt to develop that line — if the company permitted him to exercise his own judgment concerning this matter, by passively or actively acquiescing in what he did, or if the damage resulted from the direct acts of the lessees of the north dip — the defendant is not responsible for the consequences flowing from any or all of such acts. In such case the plaintiff ought only to recover the difference in the price of the coal which the defendant took from the north dip, and that which came from his own workings, as measured by the prices fixed in the two leases — we believe some ten cents per ton.

Furthermore, it will be proper for the court below to admit all such testimony as may hear upon the manner and character of the defendant’s work in the mines, and theory and intent governing it.

The judgment is reversed, and a venire facias de novo is awarded.