JURA-TRIAS IX AMERICA. 451 



Distribution of Strata. — 1. Atlantic Border. — Lying in plication- 

 hollows, or denudation-hollows, unconformably on the gneiss (meta- 

 morphic Laurentian or Silurian) of the eastern slope of the Appalachian 

 chain, are found very remarkable isolated patches of sandstones or 

 sandstones and shales, which are referred to this period. These patches 

 are strung along nearly parallel to the chain, and to the coast, from 

 Nova Scotia to the border of South Carolina. They are represented on 

 the map (p. 287) by oblique lines. One of them is found in Prince 

 Edward's Island, another in Nova Scotia ; another is the celebrated 

 Connecticut Biver Valley sandstone ; a fourth commences in New Jer- 

 sey, passes as a narrow strip through Pennsylvania, Maryland, and into 

 Virginia ; a fifth and sixth form the Eichmond and Piedmont coal- 

 fields of Virginia ; a seventh and eighth, the Dan River and Deep River 

 coal-fields of North Carolina. As they are isolated, and without con- 

 tact with any other formation unless unconformably, their age can not 

 be even conjectured from their stratigraphical relations ; but the few 

 fossils which they contain seem to refer them either wholly to the Tri- 

 assic, or else, more probably, partly to the Triassic and partly to the 

 Jurassic. 



In connection with nearly all these patches are found columnar trap 

 or dolerite ridges. These are interstratified with the sandstones, and 

 were partly outpoured on the sediments while these were depositing, 

 and partly forced subsequently between the strata (Davis). Mounts 

 Tom and Holyoke are examples in the Connecticut Valley, the Pali- 

 sades of the Hudson in the New Jersey patch ; similar trap-ridges are 

 also formed in all the other patches. 



2. Plains and Rocky Mountain Region. — The geology of this re- 

 gion is still little known, but there seems no doubt that Jura-Trias is 

 widely distributed though largely concealed by subsequent deposits of 

 Cretaceous and Tertiary. They are exposed, however, in narrow bands 

 on the flanks of the Black Hills, the Colorado, Uintah, and "Wahsatch 

 Mountains, and over wider areas in Northwest Texas, New Mexico, 

 Arizona, and Utah, where they are called " Red oeds" Their outcrop 

 form one of the most conspicuous erosion-cliffs (p. 271) of the region 

 north of Grand Caiion. As may be inferred from their almost univer- 

 sal red color, they are very barren of fossils. The same might be in- 

 ferred from the presence of great beds of gypsum in the Plateau region 

 and beds of salt in Kansas. 



3. Basin Region and Pacific Border. — They occur also over all the 

 western part of the Basin region. Covered in the valleys by recent 

 deposits, but exposed on the flanks of all the mountains. On both 

 sides of the Sierra and Cascade Ranges they occur as the auriferous 

 slates of California and northward. 



