Rothrock, J.

1. Constract: construction: evidence. I. Tbe contract which the plaintiff undertook to perforin was to construct a brick sewer in the city of Des Moines, according to certain written plans and specifications, plaintiff was to make tbe excavation, furnish tbe materials, and complete tbe work for four dollars and forty-four cents per lineal foot. He was to perform all tbe labor under tbe direction of tbe city engineer, and to furnish all tbe material necessary to construct and complete tbe work be undertook to perform. In making tbe excavation tbe plaintiff claims that it was necessary to remove a large quantity of rock in order to put the sewer in place, and that, when tbe contract was made, tbe parties thereto supposed that earth excavation would alone be required. Tbe evidence shows that tbe excavation of tbe rock imposed upon tbe plaintiff an expenditure of several hundred dollars in addition to what would have been incurred if there bad been an excavation wholly composed of earth. This is tbe foundation of tbe plaintiff’s demand against tbe city.

Tbe claim of tbe plaintiff must be determined by tbe contract, and we may here say at tbe outset that there is no ambiguity in tbe instrument that is susceptible of explanation by oral evidence. By tbe very terms of tbe contract tbe plaintiff bound himself “to furnish at bis own proper expense all necessary material and labor, and excavate and build in a good, firm and substantial manner” tbe sewer in question. It was provided in tbe specifications that “tbe contractor shall make all necessary excavations for tbe sewer proper as well as for tbe appurtenances. Tbe excavations are to be made in such directions and of such widths and depths as shall be necessary.” If these provisions of tbe agreement of tbe parties are to be construed by tbe natural meaning of tbe language employed, there is no *214ground upon which the plaintiff can be permitted to-recover. He was bound, to make the excavation without regard to the character of the substance to be removed,, whether clay, sand, quicksand, hard-pan or stone. The fact that the excavation required labor which did not enter into the contemplation of the parties when the contract was made will not excuse a performance-for the consideration agreed upon. The facts were equally within the knowledge or means of knowledge of each of the parties, and they must be held to its performance, and are not entitled to relief from hardships against which no relief can be predicated from the-agreement. Owens v. Butler Co., 40 Iowa, 190. That case was determined in 1875, and it is said therein that the principle above announced is elementary. It is .to be found in every text-book upon contracts, and why the court permitted the plaintiff to introduce parol evidence to show that both parties supposed there was-no rock formation in the line of the proposed sewer is more than we can understand. It was a plain and palpable violation of that other elementary principle that it is not competent to contradict the language of a written contract by parol evidence.

2. _._ II. But it is claimed by counsel for the appellee that the contract did not absolutely provide that rock excavations should be made. The clause relied upon is found in the specifications, and isas follows: “Whatever precaution unforeseen circumstances may render necessary in the judgment of the engineer in order to make the sewer both unyielding and impervious shall be taken; and all extra work or materials rendered necessary thereby which may be ordered by the engineer shall be paid for on his estimate, and at a price to be determined by him. Any work not herein specified, which may be fairly implied as included in this contract, of which the city engineer shall judge, shall be done by the contractor without. *215extra charge.” The first paragraph of this part of the specifications has no reference to the excavation. It refers to that part of the work necessary to make the sewer “unyielding and impervious,” and any extra labor or expense in the way of strengthening the sewer by additional courses of brick or otherwise, or by the use of additional cement or other appliance, to render the sewer impervious. It does not refer in the remotest degree to the excavation necessary to be made, and in which the sewer was to be placed. The last paragraph, in our opinion, has even less bearing upon the claim of the plaintiff than the first. It applies to any work not specified in the contract, and which is not fairly implied as included therein as extra work. But the excavation is plainly provided for in the contract. It is not necessary to imply anything to reach that conclusion. The contract is express upon this part of the work. There was no ground for any extra estimate to be made by the engineer for removing the rock, and all of his acts in that direction were without authority from the city council.

We need not discuss this case further. The court, should have excluded the parol evidence, and, instead of instructing the jury as matter of law that the plaintiff was entitled to recover, the motion of the defendant, to direct the jury to return a verdict for the defendant should have been sustained. Reveesed. .