JURA-TRIAS IX AMERICA. 



467 



teeth and bi-concave vertebrm ; but the remains are too imperfect to 

 permit distinct characterization. 



Mammals. — Lastly, in the same beds, Marsh has discovered some 

 twenty-five species of small marsupial mammals. According to him, 

 these early mammals were not typical Marsupials, but a generalized 

 type connecting that order with Insectivora. He makes of them two 

 sub-orders, Pantotheria and Allotheria. Figs. 753 and 754 are repre- 

 sentatives of these two types. 



Physical Geography of the American Continent during the Jura- 

 Trias Period. — During Palaeozoic times the Atlantic shore-line was 

 certainly farther east than it was subsequently, probably farther east 

 than it is now (p. 288). At the end of the Palaeozoic occurred the Ap- 

 palachian revolution. Coincidently with the up-pushing of the Appa- 

 lachian chain, the sea-border probably went downward, and the shore- 



Fig. 753.— Right lower jaw of Diplocynodon victor (after MarstO. outside view. Twice natural size: 

 a, canine; b, condyle; c, coronoid process; d, angle. 



line advanced westward on the land. During the Jura-Trias the 

 shore-line to the -north was still beyond what it is now, for no Atlantic 

 border deposit is visible ; and along the Middle and Southern States 



Fig. 754. — Left lower jaw of Ctenacodon serratus (after Marsh), inner view. Four times natural size. 



it was certainly beyond the bounding-line of Tertiary and Cretaceous 

 (see map, p. 291), for all the Atlantic deposits of this age have been 

 covered by subsequent strata ; and yet probably not much beyond, for 

 some of these Jura-Trias patches seem to have been in tidal connection 

 with the Atlantic Ocean. It is probable, therefore, that the shore-line 

 was a little beyond the present New England shore-line, and a little 



