Opinion,

It is very plain that the parties to this contract had in contemplation that no part of the masonry between Mahaffey and WilLiams’s Run would be first class. It was to be the same as *69the masonry between Irvona and Mahaffey, which had been constructed in the previous year, and was considered second class. The contract, in specifying the prices to be paid, made no provision for any first-class work. It is equally clear that the work was to be done “ as directed by the chief engineer ” of the company, and that “ the work was to be paid as estimated by the engineer in charge during the month, payments to be made according to that estimate about the 20th of the succeeding month, less ten per cent,” etc. Under the written contract, therefore, the engineer was the arbiter of the kind of work to be done, as well as of the class to which it belonged, and his decision determined the compensation which the plaintiff was entitled to receive under his contract. It turned out, however, that at certain points on the line masonry of a higher class and grade was required by the engineer than was contemplated by the parties, and the contract fixed no price for this higher grade of work. It is alleged on the part of the plaintiff that when this exigency arose the defendants instructed the plaintiff that the work should be done “ as directed by the engineer,” and that they would pay the plaintiff what it was reasonably worth; that the work required for arch masonry was of a superior quality and workmanship, and that the whole work as completed under the requirements of the engineer was of a better-quality than that between Irvona and Mahaffey, which was mentioned in the contract as descriptive, in a general way, of the kind of work to be done; and this suit is brought, not only to recover for “ extra ” work, that is to say, for what the work done was worth more than was stipulated in the contract, but also for the balance remaining upon the work done under the special contract.

It was undoubtedly competent for the plaintiff, by parol, to show a new and distinct agreement subsequent to the contract under seal, whereby, upon a new consideration, the original agreement was changed and the plaintiffs agreed to perform additional work, or the same work in a different manner. The rule that extrinsic evidence is not admissible to contradict or alter the written instrument is not thereby infringed: 1 Greenl. Ev., § 308; Malone v. Dougherty, 79 Pa. 53; Collins v. Barnes, 83 Pa. 15. But, in such cases, the special contract will be pursued as far as it can be traced in the intention of the parties. *70The deviation, except where otherwise expressed or mutually understood, must be taken in its proper connection with the original contract, with reference to and in modification of which it was made. The theory of the plaintiff’s case is that, according to the doctrine established in Vicary v. Moore, 2 W. 457; Spangler v. Springer, 22 Pa. 454, and other cases, to which it is unnecessary to refer, the parol agreement drew or retained the stipulations of the sealed instrument in parol, and turned the plaintiff over to his action of assumpsit for the balance due upon the entire work; that the provisions of both contracts thus became one entire parol agreement, and it is upon this ground, as we understand the case, that the plaintiff bases his right to recover Ms whole claim in this form of action. It is plain, then, that the sealed instrument must be supposed to contain the agreement of the parties to the full extent that it has not been modified by the subsequent parol contract, and that both taken together (the former being subject to the latter) state the agreement of the parties. If there had been no provision for estimates, etc., the plaintiff would, without doubt, have been entitled to recover upon a quantum meruit whatever he could show the work was worth; but all the work was to be done as directed by the engineer, and was to be paid for as estimated by the engineer in charge during the month.

The work covered by the parol agreement was the same work which was embraced in the special contract. It is alleged simply that it was to be performed in a different way if the engineer required it to be so done, and if the estimate of the“ engineer was not to determine its nature and extent it would doubtless have been so stated. The masonry was to be the same as masonry on the same line between Irvona and Mahaffey, but it was to be paid for as estimated by the engineer in charge during the month. If the work, under the requirements of the engineer, was of a higher class, it was for the engineer to determine and designate the class of work to which it belonged,, according to the usual and customary methods in railroad construction. It is not to be supposed the parties intended that the engineer, in making his estimates from time to time, was to compare in detail the work of 1887 with that of 1886, and that the compensation was to be rated accordingly. The contract provides the price to be paid for second-class work, the nature *71and characteristics of which were presumably known to the engineer; and this of itself indicates that the work was to be estimated according to a certain classification recognized in the business, and was to be compensated' accordingly. Upon that basis of calculation the defendant would be held for the difference between the value of the work required and the sum stipulated in the contract. If the parties fixed any price for the work which was required to be done in a superior manner, that price would govern in the calculation of the amount; if not, the value of this class of work could be otherwise readily shown. But the kind and classification of work was for the engineer, and his estimates, monthly and final, were conclusive upon both parties.

Although the character of the work to be performed is described, in a general way, as the same as the masonry between Irvona and Mahaffey, yet it was to be done “ as directed by the engineer of the company,” and in a good and workmanlike manner. Although, as between the contracting parties themselves, the work would be satisfactory if it was the same as the masonry between Irvona and Mahaffey, yet it was required to be done as directed by the engineer. McCauley entered into this contract with notice of the duties and powers of the company’s engineer. He took his chances with the engineer, and was to receive pay as for second-class work. It is conceded that the masonry between Irvona and Mahaffey was second-class work of an inferior quality; but this work, although of the same class, was to be performed in a good and workmanlike manner, as directed by the engineer. First-class work was not contemplated, but, when work of that class was afterwards required, the parties appear to have provided for it in a subsequent parol agreement. How much of this first-class work the engineer directed to be done, and how much was actually performed in pursuance of his direction, was for the engineer to estimate; and his certificate, fairly made, without fraud, was, by the terms of the contract, binding upon the parties. We are of opinion, therefore, that the court erred in throwing this inquiry open to the opinion and estimate of those who casually observed the work, the parties having designated a person for this purpose, a person whose classification of the work and measurement of the amount were necessarily binding in the computation *72of the plaintiff’s claim. That the parties so understood their contract is shown by the fact that monthly settlements were made upon the estimate of the engineer, and the work was paid for and receipts taken in accordance therewith. The estimates, it is true, were in some instances modified and changed, but the classification and measurement of the engineer constituted the general basis upon which these settlements were made.

It is unnecessary, we think, to consider the assignments of error in detail. If we are right in what we have said, the case was tried under a mistaken view of the nature and obligations of the contract. If, at the re-trial, the cause is conducted upon the theory suggested in this connection, the other matters assigned for error cannot arise.

The judgment is reversed, and venire facias denovo awarded.