BihUograpliical Notices. 83 



their mountain -boundarj^ and, besides ordinary sections, have pro- 

 duced some of the best sketches of geological appearances and rock- 

 scenery, and panoramic views exhibiting geological structure, that 

 any Reports have given to the public. 



" The mountains are composed of a great series of metamorphic 

 schists, gneisses, and granites of pre-Silurian ('Archaean') age, 

 with minor masses of eruptive rocks, all thrown into a complex 

 system of folds, difficult to trace on account of the absence of per- 

 manent features in any one horizon." Sihirian, Devonian (?), and 

 Carboniferous strata'are recognized in the San-Luis district. Magni- 

 ficent inversions of PaliEozoic and Mesozoic strata occur on the East 

 River (plate xvii.), and in the Madison range (Report for 1872, 

 p. 162). The unaltered strata of the great plains are all tlirown 

 up along the mountain-base, with folds and faults, their edges 

 being exposed. The lowest are the Triassic, resting on the Archaean, 

 succeeded by Jurassic, Cretaceous, and Lignitic (Upper Cretaceous 

 or Eocene), with Post-tertiary lake-beds, gravels, and lavas. In 

 " Middle Park," however, the Cretaceous seem to be the oldest of 

 the Secondary strata, and rest directly on the Archa3au ; and there 

 is observed in the district an unconformity " between the Cretaceous 

 and Lignitic formations, jiroviug that a small east and west anti- 

 clinal fold, which occurs along the Lower Grand River in the Park, 

 was formed at the close of the Cretaceous, and before the more ex- 

 tended Rocky Mountains uplift ; the inclination of probably Post- 

 tertiary lake-beds, pointing to a comparatively recent slight con- 

 tinuation of this uplift." 



Notes and resumes of these interesting formations of the N.W. 

 Territories will be found in the 'Annals,' sei". 3, vol. xi. (1863), 

 pp. 372, &c., and ser. iv. vol. vi. pp. 487, &c. 



The mining-operations in the several localities concerned are 

 described in their places in the Report ; and the minerals, especially 

 the Tellurium and TeUurides lately discovered at Gold Hill and Red 

 Cloud, are treated of in the Appendix at p. 352 &c., and by Mr. 

 Marvine and Prof. B. Silliman at pp. 685-()91. 



The special reports on Palajontology (pp. 365-536) comprise valu- ' 

 able memoirs by Professors Lesquereux and Cope. In Prof. Leo 

 Lesquereux's memoir on the Lignitic formation of Colorado and its 

 fossil Flora, the claims of these strata to be regarded as Eocene 

 rather than Cretaceous are strongly advanced. The beds with 

 Scapliites, Inocerami, &c., said to be found above, or in, the Lignitic 

 series, are regarded by some as inverted strata (p. 368) ; but the 

 continuance of some Cretaceous forms of life into the early Tertiary' 

 seas of America is regarded by Prof. Lesquereux as the real cause 

 of the apparent anomaly. 



In his memoir on the Cretaceous and Tertiary Vertebrata of Colo- 

 rado and Dakota, Prof. E. D. Cope* indicates 149 species, 94 of which 



* In the Report for 1872, Prof. Cope described, as new members of the 

 Eocene fauna of Wyomhig, about 45 species of Mammalia, 3" of Birds, 

 44 Reptiles, 1 Bitrachian. and 26 Fishes. • ■ ■ 



