Mesozoic and Ccenozolc Qeology and Paloeontologij. 93 



mura thickness ascertained from data, furnished by well-borers, is 350 

 feet. Its outcrop occupies a belt of the surface averaging about eight 

 miles wide for at least half way through the State. This Group is 

 the northern extension of the rotten limestone of Mississippi and 

 Alabama. ' 



The Ripley Group occupies a belt of the surface along the Memphis 

 and Charleston Railroad about fifteen miles wide, but having a less 

 average width across the State. The high ridges dividing the waters 

 of the Tennessee and Mississippi rivers lie mostly within its area. It 

 has a thickness of 400 or 500 feet/and is mostly made up of stratified 

 sands, though occasionally an interstratified bed of dark, slaty clay, 

 10 to 30 feet in thickness, occurs, or more frequently a sandy bed 

 laminated with clayey leaves. The hills about Purd3^ in McNairy, and 

 about Lexington, in Henderson county, show these rocks well; but 

 more interesting sections, on account of the fossils they contain, are 

 found in Hardeman, near the M. & C, R. R. 



In 1869, J, D. Whitney* divided the Cretaceous formation, which is 

 found covering large areas on the west coast, from Vancouver and the 

 adjacent islands of San Juan Archipelago on the north, through 

 Washington Territory and Oregon to Southern California, as well as iso- 

 lated patches in Eastern Oregon and in Mexico, into four groups, as 

 follows: 



1. The Tejon Group, the most modern member, is peculiar to Cali- 

 fornia, It is found most extensively developed in the vicinity of Fort 

 Tejon and about Martinez. From the latter locality it forms an almost 

 continuous belt in the Coast Ranges to Marsh's, fifteen miles east of 

 Mt. Diablo, where it sinks under the San Joaquin Plain. It is also 

 found at various points on the eastern face of the same range, as far 

 south as New Idrea, and in Mendocino county, near Round Valley, 

 the latter locality being the most northern point at which it is yet 

 known. It is the only coal-producing formation in California. 



This group contains a large and highly characteristic series of fossils, 

 the larger part peculiar Jo itself, while a considerable percentage is 

 found extending below into the next group, and several species still 

 further down into the Chico Group, Mi-. Gabb considered it as the 

 probable equivalent of the Maestricht beds of Europe. 



2. The Martinez Group, which includes a series of beds, of small geo- 

 graphical extent, found at Martinez and on the northern flank of 

 Monte Diablo. 



=-Pal. ofCaL, vol. 2, 



