F. H. Knowlton — Jurassic Flora of Oregon. 49 



United States, a profusion of identical forms such as to suggest 

 very forcibly the existence of a former land connection. 



At the present point it will be of interest to consider the 

 occurrence of Jurassic plants at various localities in Alaska, 

 the first and in many respects most important being the areas 

 along the west shore of Cook Inlet. In this area Stanton and 

 Martin* have established the Enochkin formation, the upper 

 part of which tliey regard as the equivalent of the Callovian 

 of European standards. Following German usage, this is con- 

 sidered by these authors as belonging to the upper part of the 

 Middle Jurassic, though according to the prevailing custom of 

 English geologists it belongs to the upper part of the Lower 

 Oolite. The upper two-thirds of the Enochkin formation, 

 which has a total thickness of from 1,500 to 2,500 feet, is 

 especially characterized by the presence of numerous species 

 of Cadoceras, several other genera of ammonites, belemnites, 

 etc. Associated with these shells, often being on the same 

 pieces of matrix, were the following plants : 



Cladophlebis denticulata 

 Gtenis grnndi folia 

 Hausmannia sp. 

 Dictyophyllum of. I>. obtusilohurn. 



The lower third of the Enochkin formation contains a fauna 

 very different from that of the upper portion. It is character- 

 ized by species of Stephoeroceras, Spheeroceras, Phylloceras, 

 Lytoceras, etc., the genus Cadoceras being absent, and the most 

 common forms being the several species of Inoceramus 

 described by Eichwald from this region. It is interesting to 

 note that this faima was originally referred largely, if not 

 wholly, to the Neocomian by Eichwald, and also that several 

 of its species were found to be the same as those from Queen 

 Charlotte Islands, once referred by Whiteaves to the Cre- 

 taceous. Associated with the ammonites were the following 

 plants : 



Sagenopieris Goppertiana 

 Pterophyllum rajmahalense 

 Macrotmniopteris californica. 



It is of importance to note that every one of the five named 

 and positively identified species from the Enochkin formation 

 occurs in the Oroville (Monte de Oro) flora. Several important 

 inferences may be drawn from the intimate relation between 

 the floras of these two areas. Thus, the Mariposa formation, 

 with which the Monte de Oro formation has been identified, is 

 regarded by Stanton as referable to the late Jurassic, but if a 

 *Geol. Soc. Am., Bull., vol. xvi, p. 397, et seq., 1905. 



Am. Jour. Sci.— Fourth Series, Vol. XXX, No. 175.— July, 1910. 

 4 



