Reviews — United States Geological Surmys. 413 



some of Dr. Hayden's researches (Geol. Mag, Vol. YIII. p. 32), 

 and the above Eeports, with the exception of No. 1, which is a reprint, 

 are further valuable contributions to the geology of the north-west 

 districts explored. Besides the special geology, they contain remarks 

 on the physical features, notices of the various economical substances, 

 descriptions of the fossils, together with catalogues of Mammals, 

 Shell?, Insects, and Plants, collected during the expeditions. 



The Sixth Report (No. 4) is full of interesting matter, and well 

 worthy of the studj'^ of the European geologist, both as regards physical 

 geology and palteontology. It includes descriptions of the Yellow- 

 stone Valley, and adjacent country, — the canons, the thermal springs, 

 the geyser basins, etc. The formations noticed are G-neiss, Silurian, 

 Carboniferous, Jurassic, Cretaceous, and Tei'tiary. These strata are 

 described by Mr. A. C. Peale as well seen in the Gallatin caiion, 

 situated between the two great rivers, the Yellowstone and the 

 Madison, which is a continuous gorge cut by the river for more than 

 seventy miles, with walls rising on either side from 1000 to 2000 ft., 

 exposing a geological section which has hardly a parallel in the 

 North-west. 



The student of ' Earth Sculpture,' conversant with the enor- 

 mous amount of denudation which certain areas of Great Britain 

 have undergone, will read with interest the following lines in Dr, 

 Hayden's Eeport, p. 43 : — " The evidence becomes stronger every 

 year of exploration that the erosive forces have acted on a more 

 stupendous scale than I had ever conceived or expressed in any of 

 my former Reports ; that the entire series of sedimentary strata, from 

 the lowest Silurian to the highest Tertiary known in the west, has 

 extended in an unbroken mass all over the North-west ; and we find 

 here and there, by the exposure of the entire series, as at Cinnabar 

 Mountain, and in many other localities, the most satisfactory proof 

 of the statement which I have so often made. This single state- 

 ment implies that from 10,000 to 15,000 feet in thickness of un- 

 changed rocks have been removed from this mountain region, except 

 what might be called remnants left behind, occupying restricted 

 areas. The older the group, the larger the area over which it has 

 escaped erosion. The hard and compact limestones of the Silurian 

 and Carboniferous ages are found to a greater or less extent all over 

 the North-west. They yield much less readily than the more modern 

 beds, and are consequently found ou the summits of the highest 

 mountains, 10,000 and 12,000 feet above the sea." 



Again, the geologist conversant with the evidence of contempo- 

 raneous volcanic action in the Tertiary period of the British Islands, 

 as seen in Northern Ireland, Scotland, and the Western Isles, so 

 fully described by Prof. Geikie and Mr. Judd, will find a pai-allel in 

 the proofs of similar volcanic activity, and apparently of the same 

 age, intensity, and extent, in the Western territories of the States. 

 Dr. Hayden remarks : " I am now inclined to believe that when our 

 western country is more thoroughly explored by competent geologists, 

 it will be found that the area covered with volcanic rocks is far 

 greater than we have hitherto suspected. Like the more modern 



