468 MESOZOIC ERA— AGE OF REPTILES. 



beyond the old Tertiary shore-line of the Middle and Southern Atlan- 

 tic States. 



A little back from this shore-line, and at the foot of the then Ap- 

 palachian chain, there was a series of old erosion or plication hollows 

 stretching parallel to the chain. The northern ones had been brought 

 down to the sea-level, and the tides regularly ebbed and flowed there 

 then as in the bay of San Francisco, or Puget Sound, at the present 

 time. In the waters of these bays lived swimming Eeptiles, Croco- 

 dilian and Lacertian, and on their flat, muddy shores walked great 

 bird-like Eeptiles, and possibly reptilian Birds. The more southern 

 hollows seemed to have been above the sea-level, and were alternately 

 coal-marsh and fresh-water lake, emptying by streams into the At- 

 lantic. Since that time the coast has risen 200 or 300 feet, and these 

 patches are therefore elevated so much above the sea- level. 



Meanwhile, somewhat similar changes were going on in the western 

 portion of the continent. During Palaeozoic times, the Pacific shore- 

 line was just east of the Sierra Eange, and the place of this range was 

 a marginal sea-bottom. At the end of the Palaeozoic, coincidently with 

 Appalachian revolution already explained (p. 409), the Utah Basin 

 region was elevated and became land, while the Nevada Basin region 

 subsided, and the Pacific shore-line advanced eastward to Battle Mount- 

 ain. But the whole area between this Basin region continent and the 

 Palaeozoic area of eastern North America, including the Plateau region 

 and the Plains region, was covered by one or more shallow inland seas, 

 with imperfect connection, or none at all, with the ocean, and in which, 

 therefore, gypsum and salt deposited by evaporation. At least once dur- 

 ing Jurassic times this inland sea became broadly connected with the 

 ocean, so that oceanic conditions prevailed. The place now occupied 

 by the Wahsatch Mountains was then a marginal sea-bottom, bordering 

 the Basin region continent. On the west the Pacific shore-line was 

 some distance east of the Sierra, and the place of that range was still a 

 sea-bottom, though not so closely marginal as in Palaeozoic times. 



Disturbances which closed the Period. — This long Jura-Trias period 

 was closed, and the Cretaceous period inaugurated, by the Sierra revo- 

 lution, by which the sediments accumulated along the then Pacific 

 shore-bottom, yielding to the lateral pressure, were mashed together 

 and swollen up into the Sierra and Cascade Eanges, and the coast-line 

 transferred westward to the other side of these ranges. Coincidently 

 with this change probably occurred on the Atlantic slope the elevation 

 of the Jura-Trias sounds and the outbursts of igneous matter, forming 

 the trap-ridges already spoken of (pp. 451 and 452). Extensive changes 

 also occur at the same time over the whole region of the inland seas, by 

 subsidence and the inauguration of oceanic conditions, which continued 

 to prevail during the Cretaceous. There is reason to believe also that 



