“ The suit proceeds upon the theory that a contract between the owners of the roads, entered into before the enactment of the statute upon which the order rests, imposes upon the junior road all the expense of maintaining and guarding the crossing, in whatever manner may be essential to make its use safe and convenient, and that the order, by imposing a part of the expense of its execution upon the other road, impairs the obligation of the contract, and therefore is void. ”

“ See Chicago, B. & Q. R. Co. v. Nebraska, 170 U.S. 57, 71-74, 42 L. ed. 948, 953, 954, 18 Sup. Ct. Rep. 513; New York & N. E. R. Co. v. Bristol, 151 U.S. 556, 567, 38 L. ed. 269, 272, 14 Sup. Ct. Rep. 437. ”