S7i^ Bihliogrdphical Notice. 



where supposed to have hecome extinct at the close of the CTretaceous 

 epoch, we would be in doubt whether to pronounce them Tertiary 

 or Cretaceous," the associated fossils being " more closely allied to 

 Tertiary types than Cretaceous" (pp. 30 & 128). 



VIII. The Tertiary formations in the north-west are divisible into 



1 (uppermost). Yellow marl (Loess). 



2. White River group. 



3. "Wind River Valley group, 



4. Lignitic group. 



5. Estuary group. 



The "Estuary-group," of which the Judith Basin maybe regarded 

 as the type, is widely distributed (p. 126), These beds are found at 

 the sources of the Moreau, Grand, and Cannonball Rivers ; and at 

 the mouth of the Big Horn they are 800 to 1000 feet thick. Similar 

 deposits occur on the west side of the mountains near Green River. 

 The "Estuary Beds" pass up gradually into the Lignitiferous group, 

 the mingled brackish and freshwater shells giving place to terrestrial, 

 lacustrine, and fluviatile forms, which alone, without any marine 

 associates, are found in the Upper Tertiaries of these vast regions. 

 Some dicotyledonous leaves and silicified wood occur in some of the 

 Estuary-deposits, but are insufficient "to indicate the great luxu- 

 riance of vegetation which must have existed during the accumula- 

 tion of the Lignite-strata" (p. 126). In the body of the memoir 

 (p. 92) these two groups are described together under the heading 

 " Great Lignite Tertiary basin." Silicified trunks of trees, 50 to 

 100 feet in length, occur abundantly over hundreds of square miles 

 along the Missouri and Yellowstone Rivers, in the Lignitic Tertia- 

 ries ; and there are from thirty to fifty beds of lignite, varying in 

 thickness from 1 inch to 7 feet. The lignites on the Yellowstone 

 River and elsewhere have been much affected by spontaneous com- 

 bustion (p. 99). The Vertebrate remains as yet obtained from the 

 Estuary and Lignite groups belong to Thespesius occidentalis, Ischy- 

 rotherium antiquum, Mylognathus priscus, Compsemys victus, and 

 Emys obscurus, all described by Leidy in Proc. Acad. Sc. Philad. 

 1856, and Trans. Americ. Phil. Soc. 1859. The list of the other 

 fossils is given in pages 101-103 of the memoir. These interesting 

 Tertiary beds have an enormous geographical extent. Dr. Hayden is 

 of opinion that they reach from the Arctic Sea to the Isthmus of 

 Darien along the Rocky Mountains, with the elevation of which they 

 have partaken (pp. 118 & 126). 



The Wind River group is from 1500 to 2000 feet thick, is inter- 

 mediate in character between the foregoing and the next group, 

 occurs on both sides of the mountains, and has partaken in the ele- 

 vating movements, but in a less degree, having probably been formed 

 whilst the uprising took place (p. 127). 



The White River group is of great extent, on both sides of the 

 mountains, overlies the Lignite group, and has a nearly horizontal 

 postion, whilst the Lignitiferous beds are much inclined (pp. 127, 

 i 28) : these facts were not clearly recognized when the first part of 



