F. GEOGRAPHY. 291 



been considered volcanic. If these latter rocks are also in 

 the present case metamorphic, the fact will be an important 

 addition to volcanology. Captain Dutton is also engaged in 

 the investigation of the micro-structure of the rocks of this 

 region, and has made considerable progress in the preparation 

 of specimens for microscopic examination. 



At the beginning of the fiscal year Professor C. A. White, 

 of Bowdoin College, was appointed paleontologist of the 

 Division, and he immediately joined Major Powell's special 

 party, mentioned above. This party visited many points in 

 Northern Utah, a few in Northwestern Colorado, and a few in 

 Southern Wyoming, making a re-examination of the sediment- 

 ary beds of that region, and the evidences upon which they 

 had been previously separated into groups. Many localities 

 where fossils had been obtained in previous years were visit- 

 ed, and other localities discovered. The collections made 

 were from the upper portions of the Carboniferous group, 

 through the whole series to near the summit of the Tertiary. 

 The collections are chiefly of invertebrate fossils, and are 

 very full and satisfactory. 



Many new species, and also several types hitherto unknown 

 in American strata, have been obtained. Among the latter 

 may be mentioned a species of Unio, of the recent type of U. 

 clava, Lam., and two types of Viviparine shells from near the 

 base of the Tertiary, the layers containing them alternating 

 with others containing Ostrea and other brackish-water forms. 

 These facts, in connection with others already known, show 

 that much differentiation had taken place in those families 

 respectively very early in the Tertiary period, if not before. 

 It is an interesting fact, also, that while a change from a salt 

 or brackish water condition of the earlier Tertiary deposits 

 to a wholly fresh-water condition took place without pro- 

 ducing any perceptible physical change in the character of 

 the strata, the species, mostly molluscan, were more nume- 

 rous, and the differentiation of types much greater during the 

 prevalence of salt in the water than at any subsequent time 

 after the waters became wholly fresh. His notes also show 

 that in all the purely fresh-water strata of all the Tertiary 

 groups the species and genera are few, and there is a remark- 

 able uniformity of type throughout. Both branchiferous and 

 pulmonate mollusks range through all the Tertiary strata, 



