“ But, as it makes no mention of such lands, it is permissible-indeed, is essential-to inquire whether the congressional will is otherwise made manifest, that is to say, whether the general words of the grant are to be read in the light of other statutes and a settled public policy in respect of mineral lands.
In the legislation concerning the public lands it has been the practice of Congress to make a distinction between mineral lands and other lands, to deal with them along different lines, and to withhold mineral lands from disposal save under laws specially including them. ”

“ The conditions ensuing from the discovery of gold and other minerals in the western states and territories resulted in a general demand for a system of laws expressly opening the mineral lands to exploration, occupation and acquisition, and Congress, responding to this demand, adopted from 1864 to 1873 a series of acts dealing with practically every phase of the subject and covering all classes of mineral lands, including coal lands. ”

“ While the early land laws occasionally and specially provided for the sale of mineral lands, they very generally evinced a purpose to reserve such lands for future disposal; and this purpose was given particular emphasis following the discovery of gold in California in 1848, as is shown in the Oregon Donation Act, the Homestead Act (which adopted the mineral land reservation of the Pre-emption Act of 1841) , the grant to the several states for the benefit of agricultural colleges, the railroad land grants and other land acts of that period. ”