652 NORTH AMERICAN INDEX FOSSILS. 



Bathonian : representation not definitely known. 

 Bajocian : represented by the Mormon sandstone of 



Shasta County, Cahfornia, and in part perhaps by the 



Tordrillo series of the Alaska Range. 



LOWER JURASSIC OR LIAS (in broad sense). 



ToARCiAN : represented by the Hardgrave sandstone of 

 Shasta County, California, and by equivalent beds of 

 Nevada and Alaska. 



LlASSIAN "1 



SiNEMURiAN I (representation not definitely known). 

 HettangianJ 



Of Jurassic age but doubtful correlation, are further a number 

 of non-marine deposits of the Rocky Mountain region, especially 

 such as the La Plata and overlying McElmo formations lying 

 between the Dakota and the Triassic in the San Juan district of 

 Colorado, and the White Cliff (Lower Jurassic) and Flaming 

 Gorge group (Upper Jurassic) of Arizona and Utah, the latter 

 marine, as is also the Ellis formation of the Yellowstone. 



On the Atlantic coast, the lower two divisions of the Potomac 

 Group, the Patuxent (lowest) and Arundel (upper) are referred 

 to the Jurassic. 



X. The Comanchic System. 



The Comanchic system is typically developed in the Gulf region 

 of North America, and in the Pacific coast. In the former region, 

 the three- fold division is : 



3. Upper or Washita (or Washitan). 



2. Middle or Fredericksburg (or Fredericksburgian). 



I. Lower or Trinity (or Trinitan). 



The Trinity division comprises in descending order : Paluxey 

 sands, Glen Rose limestone and Travis Peak beds (including 

 Hensel sand and conglomerate, Cow Creek beds and Sycamore 

 sands). 



The Fredericksburg is divided in descending order into the 

 Edwards limestone, Comanche Peak limestone, and Walnut clay. 

 The latter often replaces some of the limestones, and in northern 



