Ladd, J. —
The alleged lease to the Crescent Coal Company dated October 10, 1906, ivas assigned by it to the plaintiff July 10, 1907. The instrument, which for convenience may be designated the first lease, purported to be from the widow and heirs.of William A. Littlejohn to the former company; but neither it nor two of the heirs ever signed such instrument, and the guardian of a minor heir had signed his name thereto without ,an order of court. The lease executed April 30, .1907, by the widow and heirs to Miller and McMillan, and by them assigned to Love, is not challenged save as purporting to permit *223the removal of coal previously disposed of by virtue of the first lease ' under which plaintiff claims.
1. Landlord and ?£ses féxecuevidence. The controlling question is whether the instrument of May 10, 1906, was binding on the parties thereto at the time the second lease was executed. Appellees contend that the first lease was never executed, and that, if it was, it was subsequently abandoned. The evidence is conclusive to the effect that Crew, representing the Crescent Coal Company, and the widow and heirs in negotiating the lease, expressly agreed orally that the instrument should not be binding on the parties thereto until signed by -all the heirs and the company and a copy signed by the company was returned to them. As two of the heirs and the company failed to sign the paper, it never was executed. Appellant, however, argues that oral evidence’ of the arrangement under which part of the heirs signed was not admissible because tending to- vary or contradict a written contract. Such was not the purpose of the evidence, but rather to show that the writing never became obligatory at all, and to do that it was competent. Sutton v. Weber, 127 Iowa, 361; Creveling v. Banta, 138 Iowa, 47.
2. Leases: unilateral contract. But appellant contends that it should be treated as a unilateral agreement. Such was not the intention of the parties, for, apart from the oral arrangement referred to, by the terms of the lease obligation to work the mine and pay rent or royalty are imposed on the lessee, and the instrument stipulates that the parties are to bind themselves by signing the lease. As it was not so intended, the lease should not- be construed as unilateral. Flanders v. Merrill, 38 Iowa, 583; Cross v. Snakenberg, 126 Iowa, 638.
*2243. Mines and mining: leases: acceptance. *223Nor was such lease accepted and adopted by the parties as to render it binding. True, the lessee was to “test said' land by drilling and otherwise, and, in- case there *224should be discovered a minable vein or basin of coal of sufficient quantity and quality to justify the opening and mining of said coal in the opinion of said party, then they agree to mine out said coal,” and pay as stipulated. In other words, it was optional with the company whether it should mine the underlying coal, and it was allowed to prospect in order to enable it to elect whether it would do so. It went upon the land for the purpose of investigation, and not in pursuance of an agreement to mine. Such possession neither bound it to proceed under the lease, nor was it notice of acceptance to the lessors. In prospecting coal was discovered in workable quantities, but the company never so advised the lessors. Indeed, the president of the company testified that “the Crescent Coal Company had never made up its mind as to what it would do,” and, believing it “a better proposition to sell the lease than to open the miné,” assigned the lease to plaintiff. In so far as disclosed by the record, it may still be in this condition of uncertainty. As it had neither signed the lease nor accepted its terms, the paper never became binding on the parties thereto. The widow and heirs could not have enforced the terms of the lease. Love v. Atkinson, 131 N. C. 544 (42 S. E. 966); Castro v. Gaffey, 96 Cal. 421 (31 Pac. 363). Nor could the Crescent Coal Company without signing and electing tc proceed to mine coal thereunder. Ordinarily time is held to be of the essence of mining contracts, even though not expressly so stated, and parties thereto must be vigilant-in asserting their rights thereunder. See Merk v. Bowery Min. Co., 31 Mont. 298 (78 Pac. 519); Waterman v. Banks, 144 U. S. 394 (12 Sup. Ct. 646, 36 L. Ed. 479). Whether there has been such delay in this case as to defeat the contract need not be considered, as the lease never became binding on either party thereto, and nothing passed under the alleged assignment to plaintiff.
*225What- we have said sufficiently answers the contention that the lease, as it were signed by the widow, a life tenant, was valid.
The petition was rightly dismissed, and the judgment i,s affirmed.