proposed will have an important influence on the progress of geology, especially in this country.
The publication of Mr. King's volume certainly throws a flood of light on the complicated and hitherto somewhat chaotic geology of our Western Territories, and it can not fail to afford important aid in the proper orientation of both observers and observations in all the great region west of the Mississippi.
It is evident that nothing like a thorough discussion of the facts and conclusions contained in Mr. King's great volume of eight hundred quarto pages can be given here; but some of the most important of his facts, and the more interesting of his generalizations, will be briefly noticed in the succeeding pages.
Archæan.—By this term, which he accepts from Dana, Mr. King designates all the great mass of crystalline schists and granitoid rocks which underlie the Cambrian system, and form the base of his grand section. These are most fully exposed in the Park and Medicine Bow Ranges of Colorado and Wyoming, and in the Humboldt and Truckee Mountains of Nevada; but there are also numerous minor ranges and summits composed of granitoid rocks, especially west of Salt Lake; and Mr. King shows that these latter exposures are portions of a broad pre-Cambrian land-surface which formed the western border of a great topographical basin that reached to the Rocky Mountains on the east. This basin was occupied by the seas from which were deposited the Palæozoic rocks. These latter were largely derived from the erosion of the neighboring land on the west, and formed a conformable series, of which the estimated thickness is over 30,000 feet. The old land which supplied the mechanical material of the Palæozoic strata extended to an unknown distance northward, and reached southward at least to the present head of the Gulf of California, in a region where it was recognized by the writer, and its relations to the Palæozoic series of the Colorado plateau pointed out in the "Report of the Colorado Exploration," 1861.
Mr. King divides the Archæan rocks into two great groups, of which the first consists at base of gray or flesh-colored bedded granite, overlain by red, massive granite, on which lie red, micaceous, bedded granites, the whole attaining a thickness of perhaps 25,000 feet. This group is characterized by the presence of quartz, orthoclase, and oligoclase feldspars, with a little hornblende and mica, the latter consisting of biotite, muscovite, and lepidomelane. It also contains more or less labradorite, titaniferous iron, magnetite, and graphite, the whole corresponding closely with the Laurentian of Canada.
The upper subdivision of Archæan rocks—found in the Medicine Bow and Park Ranges, the Uintah, Wahsatch, Humboldt Mountains, etc.—consists of true gneisses, interstratified with mica schists, often garnetiferous, hornblende schist, sometimes with zircon, etc., all very distinctly, often minutely stratified. The thickness of this group is in
