Thick sequences of silicate and carbonate rocks of sedimentary origin have been investigated in 64 areas in North America. The areas containing the thickest and most homogeneous stratigraphic sections more than 1,000 feet thick, buried at depths greater than 10,000 feet are:
1. Uinta Basin, Utah, where the Mancos shale is 1,300 to 5,000 feet thick, the Weber sandstone is 1,000 to 1,600 feet thick, and Mississippian limestones are
1,000 to 1,500 feet thick.
2. Washakie Basin, Wyoming, and Sand Wash Ba.sin, Colorado, where the Lewis shale is 1,000 to 2,000 feet thick and the Cody-Mancos shale is 4,500 to 5,500 feet thick.
3. Green River Basin, Wyoming, where the Cody-Hilliard-Baxter-Mancos shale sequence averages more than 3,000 feet, the siltstone and shale of the Chugwater formation totals 1,000 feet, and the Madison limestone ranges from
1,000 to 1,400 feet thick.
4. Red Desert (Great Divide) Basin, Wyoming, where the Cody shale is 4,000 feet thick.
5. Hanna Basin, Wyoming, where the Steele shale is 4,500 feet thick.
6. Wind River Basin, Wyoming, where the Cody shale is 3,600 to 5,000 feet thick.
Geochemical characteristics of these rocks in these areas are poorly known but are being investigated. A summary of the most pertinent recent ana1yses is presented.