FEATURES IN HISTORY OF LIFE ON PACIFIC COAST 



The plants of the last two periods preceding the 

 present, that is the Pliocene and the Pleistocene, are 

 relatively little known, though scanty materials have 

 been obtained from formations of both periods. 



HISTORY OF INVERTEBRATE FAUNAS. The unusually 

 thick series of sediments in the Pacific Coast region 

 presents an exceptional opportunity for the study of 

 life zones of invertebrates. The marine faunas of a 

 number of the periods are at least as well repre- 

 sented here as in any part of the world, and some 

 of the faunas are of unusual importance. In the 

 western region the faunas of the Silurian and De- 

 vonian are not relatively significant. Jurassic faunas 

 are known, but are of relatively small importance. 

 The Carboniferous and Permian are represented by 

 abundant remains at a number of localities. The 

 Cambrian, Triassic, Cretaceous, Eocene, Oligocene, 

 Miocene, Pliocene, and Pleistocene are all known by 

 faunas of unusual interest which may well attract 

 the attention of the palaeontologist. 



Cambrian faunas are found at a number of locali- 

 ties in the western region, among those of import- 

 ance being the occurrence of Lower Cambrian in 

 Inyo County, California, and the extraordinary Cam- 

 brian faunal representation of southern British Co- 

 lumbia. The occurrence at Field, in British Colum- 

 bia, is among the most important of the Cambrian 

 localities of the world. The wonderful preservation 

 of the specimens makes possible unusually satisfac- 

 tory studies on this fauna. The slab shown in Plate 

 IX illustrates the nature of the material. 



Silurian rocks are known in Plumas County, Cali- 

 fornia. A Devonian fauna has been obtained from 

 limestones exposed along the upper Sacramento 

 River at Kennett. Carboniferous exposures of im- 

 portance appear in Shasta County, California, where 

 great thicknesses of shales and limestones contain in 

 places an abundant fauna. 



Of the whole Pacific Coast section there is no 

 division in which the invertebrate life is of 

 greater interest, or presents a greater variety of 

 forms than the Triassic of Idaho, Nevada, and Cali- 

 fornia. Through the work of Professor James Per- 

 rin Smith these faunas have been exhaustively inves- 

 tigated, and a part of the result of this work has 

 already appeared in the publications of the United 

 States ^Geological Survey. By far the most interest- 

 ing phase of the Triassic life represented in these 

 rocks is found in the nautilus-like molluscs of the 

 ammonoid group, which are known by a great num- 

 ber of specimens representing many genera and 

 species, and showing a remarkable state of preserva- 

 6 



