Opinion by

While the contract which is the subject of construction in this case grew out of the attempted drilling by defendants of a single well through plaintiff’s intervening seam of coal, its manifest purpose was to set at rest not only the existing dispute in respect of that particular well, but other wells which defendant should desire to drill under their lease. If oilshould be developed in paying quantities by that well, they would of course drill other wells to the exhaustion of that field, and provision would therefore naturally be made for them in order to avoid a repetition of the difficulties. The subject of the contract was a right of easements, in indefinite series, which were essential to the development of defendants’ leasehold property and whose regulation was necessary to the safe operation of plaintiff’s mines : *554and it was to the advantage of both parties that their disputes should be adjusted at once and for all. Hence it was expressly stated that tire contract was made for the “purpose of settling and adjusting all differences between them: ” and among the differences so settled and adjusted was the payment by defendants to plaintiff of a stipulated sum for the well then being drilled, out of which the dispute had arisen; but “ in addition thereto ” a like sum for “ each additional well drilled upon said land ” thereafter. It is conceded that the defendants were bound for the payment of the sum stipulated so long as they themselves continued to drill; but not after the assignment of the leasehold. Why not so long as wells should be drilled under their contract ? “ Additional wells ” have since been drilled; and defendants’ promise was absolute and unqualified to pay for them in the manner stipulated. The contract was, on the part of defendants, in effect an agreement to purchase, from plaintiff, rights of way 'involving an element of personal responsibility which could not be avoided by any ex parte act of theirs. Their status cannot'be distinguished from that of any other purchaser, of an interest in land, who has made himself personally liable for purchase money. The contract was mutual; and neither party could modify it without the assent of the other. It is not alleged that plaintiff has given any express assent; and it does not appear that it has done anything from which an implication of assent can be drawn. The assignment upon which defendants rely was purely ex parte, and is a “new way of paying old debts ” which no court of justice can recognize. They continued liable, “ because, although their assignment had divested them of the lease, it could not relieve them of their contract” with plaintiff: Washington Nat. Gas Co. v. Johnson, 123 Pa. 592.

It" was suggested that plaintiff’s recognition of the assignee’s status operated as a release of defendants’ liability, but defendants’ assignment was the exercise of a right, incident to ownership, which plaintiff had no power to prevent, and which had no relevancy to the question of liability as between them.

So it was argued that because plaintiff had failed to demand from the assignee the sum stipulated for each well when begun, it was guilty of laches which worked a forfeiture of its right to claim: but the time of payment, being for its benefit, might be *555waived, whereas the burden of payment having been on defendants, the default was theirs.

It follows, therefore, that there was no error in entering judgment, in favor of plaintiff and against defendants, for want of a sufficient affidavit of defence.

Judgment affirmed. .