3 o5 THE POPULAR SCIENCE MONTHLY. 



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 hun- 

 dred 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. 



Archaean. 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 

 Palaeozoic rocks. These latter wei'e 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 Palaeozoic strata ex- 

 tended 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 Palaeozoic 

 series of the Colorado plateau pointed out in the " Report of the 

 Colorado Exploration," 1861. 



Mr. King divides the Archaean 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 oligo- 

 clase 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 cor- 

 responding closely with the Laurentian of Canada. 



The upper subdivision of Archaean 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 



