The uncertainty peculiar to all undertakings of this kind in the United States, arising from the necessity of appealing to each successive Legislature for the means of carrying on the work, and the disturbed state of the country during the whole time since we commenced operations, as also the unfortunate condition of the finances of the State, which has kept the treasury from one to two years behind in the payment of the legislative appropriations, have combined to render it difficult to arrange and carry out as systematic a plan for the conduct of the work as would, under more favorable circumstances, have been practicable. Two ideas have, however, as far as possible, governed the survey in its operations: the first was, to make, as rapidly as could be done, a reconnoissance of the State, with the view of acquiring a knowledge of its general geological structure, the age of the various formations which occur in it, and as complete a general idea as possible of their range and extent, so that a foundation might be laid for the detailed work which would follow the preliminary examination; the second idea was, at the same time that the general examination was going on, to work up in detail certain more important districts, so that the public might have light on questions of economical interest, and at the same time be able to form an idea of what the work might be if ever carried to completion. Besides this, the natural history part of the survey was to be carried on, in connection with the geological work, as rapidly as possible, progress in all departments being necessarily proportioned to the varying amounts of the annual appropriations. California is covered by a vast net-work of mountain ranges, separated by comparatively narrow valleys, with the exception of those of the Sacramento and San Joaquin, which do not, together, cover more than one-fifteenth of the area of the State. The remaining fourteen-fifteenths may be called mountainous, as the valleys include but a small portion of its surface. Into this mountainous region no accurate surveys have ever been carried; even the General Land Office work stops at the base of the mountains. A few ranch lines have been run among the moderately elevated portions of the Coast Ranges; but, as a general thing, the genuine Mexican grants were limited to the plains.