REVIEWS. 
293 
'Thomomys winch compose it, and a comparison of the cranial characters of 
this family with the Saccomvidse, in which, notwithstanding the close affinity 
of the two families, their crania are curiously different in general appearance 
-and details of contour. A valuable synopsis is given of insectivorous mammals 
based on the relations of the study of the American forms and their com- 
parison with those of other parts of the world, and preceded by a notice of 
the classification and views of the various authors who have written on this 
.group. A report on the mollusca of Colorado concludes this number. No. 3 
contains a topographical and geological report, including the mines of 
San Juan country, by Messrs. Wilson, Bhoda,and Endlich. From the report 
of the latter it appears that more than 4,500 square miles of the country is 
covered, in one continuous area, by volcanic rocks, the character of which 
throughout the district is one of extreme interest, demonstrating an enor- 
mous amount of activity during probably a short period of time, but which 
was, nevertheless, accompanied by a comparatively large number of changes 
in the chemical and physical qualities of the ejected material, and which 
consist mainly of variously coloured trachytes, sometimes with interstrati- 
fied obsidian ; these trachytes, of an aggregate thickness of 7,000 feet, forming 
the main mass of the volcanic rocks, are succeeded, but not continuously, by 
beds of rhyolite, dolerite, and basalt. With regard to the metallic lodes of 
the district, they appear to be, geologically speaking, young, probably having 
been formed at the close of the cretaceous or the beginning of the tertiary 
period, for they run through the trachytic rocks (which are supra cretaceous) 
in a very straight and regular course, either north-east to south-west or the 
reverse. The mines are but in their infancy, and the ores mainly found are 
galena, sphalerite, pyrite, chalcopyrite, fahlerz, and the variety freibergite. 
The same author, Mr. Endlich, contributes in the Report for 1873 a paper on 
the mining district of Colorado, with a catalogue of the minerals, including 
native tellurium, and the geology of the San Luis district, from which it 
appears that granitic and volcanic rocks constitute the two main systems of 
mountain ranges which traverse the country ; a narrow band of silurian and 
carboniferous beds traverse the central portion of the districts in a south- 
easterly direction. Mesozoic and tertiary strata are found only along the 
eastern edge of the Front range, the cretaceous extending into the moun- 
tains in a few bays of ten to twelve miles in length, while the drift covers 
the San Luis valley and other portions of the district. Besides this paper, 
the report of more than 700 pages, with many plates, by Dr. Hayden shows 
the continued activity and labours of himself and his colleagues in the ex- 
ploration of the district under his charge, from which much additional in- 
formation of a detailed character is given of the geology, mineralogy, palae- 
ontology, zoology, and mining industry of the parts of Colorado surveyed 
during the past year. Dr. E. Cope describes the vertebrate fossils of 
Colorado, in which he briefly discusses the mutual relations of the cretaceous 
and tertiary formations of the West; a subject also alluded to by Professor 
Lesquereux, in his able and instructive paper on that debatable ground 
the lignitic formations of the West. They are referred by him to the tertiary 
period, although some cretaceous animal remains have been found with them. 
The tertiary aspect of the lignitic flora is undoubted, and their affinity to the 
tertiary flora of Europe ; but they differ from the Dakota group below, from 
