AGE OF THE KO(yrENAI 339 



partially revised by nie in my study of the Lower Cretaceous Horn of 

 Maryland and Virginia, comprises 86 species in 42 genera. Thirty-rour 

 of these genera occur in the Lower Cretaceous of the Atlantic Coastal 

 Plain. 



Of these 86 recorded forms from the Kootenai, 13 are so poorly ])re- 

 served that they have never been specifically determined, although I'i of 

 the genera to which they are referred are commonly represented in the 

 Potomac. There are 31 species not yet discovered outside of the Xoolt'niii 

 deposits. These represent 24 genera, of wliich 18 ai'e iv])resentc(l in ihc 

 Potomac, several being confined to its uppermost foruuition, the l'ala])S(o, 

 which is clearly of Albian age. 



Deducting the foregoing 44 species from the Kootenai total, there re- 

 mains 42 species, or nearly 50 per cent, with an outside distribution. 

 Before considering the significance of these forms \nth an outside dis- 

 tribution, there remains to be ruled out of the discussion the following 

 forms that are without stratigraphic or chronologic significance for the 

 reasons noted in connection with each: 



Dawson identified two species of Ginkgo with forms described originally 

 by Heer from tlie Upper Oolite of Siberia. These really represent a 

 single species, and without the aid furnished by a known geologic horizon 

 they can not be distinguished from Ginkgo leaves found as late as the 

 Eocene. Another species, Podozaniites lanceolatus, possibly composite, 

 has a recorded range from the Jurassic to the top of the Upper Cretaceous 

 and is obviously of no value in correlation. Similarly Sequoia reichen- 

 bachi, also possible composite, has a recorded range from the Portlandian 

 to the top of the Upper Cretaceous, and has no chronologic value except 

 as indicative of Mesozoic age. 



'fhis leaves 38 forms possessing chronologic significance. Twenty-five 

 of these occur in the Lower Cretaceous of the iVtlantic Coastal Plain, 

 and of these 25, 19 range from the bottom to the top of the Potomac 

 group, namely, from Neocomian to Albian, in terms of the standard 

 European section. Only five are confined to the older Patuxent and 

 Arundel horizons and 21 occur in the Patapsco formation, of Albian age 

 and overlvin"" unconfonnahlv the Arundel formation oi- horizon of the 

 I'otonuic reptilian fauna. 



This, it seems to me, is an important fact, namely, that over 55 ])er 

 cent of the Kootenai species with an outside distribution are found in 

 the Atlantic Coastal Plain unconforinahly overlying the Potomas dino- 

 saurian fauna, which by hoth Marsh and Lull is said to show a distinct 

 Morrison character. Whatever modern nu'thods of comparison may make 

 out of this faunal resemblance, it was sufficiently marked, according to 



