590 A. W. GRABAU TYPES OP SEDIMENTARY OVERLAP 



begin with basal sands and conglomerates. More than two-thirds of the 

 formation is limestone, and it is succeeded by 600 feet of Glen Rose lime- 

 stone, the Palnxy being undeveloped as a sandstone. At Twin mountain, 

 in Erath county, Texas, the Glen Rose is a slightly siliceous limestone 

 5 feet thick, and is inclosed between 115 feet of basal sands and conglom- 

 erates and 190 feet of Paluxy sands. At Decatur, Wise county, nearly 

 100 miles northeast along the strike from the preceding locality, the 

 merest trace of the Glen Rose limestone appears between 200 feet of basal 

 sand and 125 feet of Paluxy. This indicates the uniform thinning north- 

 westward of the formation, largely by disappearance through overlap of 

 the basal members. The age of the basal bed at the localities of the last 

 two sections is clearly Glen Rose, though, as will be shown later, it is 

 nearer the middle than the upper part of the formation. 



Along the Texas-Indian Territory line the Trinity beds have disap- 

 peared by overlap of the Fredericksburg. Here the basal bed is known as 

 the Antlers sands, and, though spoken of as Trinity by Hill, clearly be- 

 longs in the Fredericksburg, since the overlying limestone (the Goodland) 

 is only 25 feet thick, whereas the Comanche Peak and Edwards lime- 

 stones, which it represents, are 350 feet thick in the Austin region and 

 approximate 700 feet on the Rio Grande. In western Texas, in New 

 Mexico, and in southern Kansas,* the upper Fredericksburg beds are 

 represented only by shore-derived elastics. In southern Kansas they are' 

 the plant-bearing Cheyenne sandstone, which rest directly upon the Red 

 beds (Permian) and have a thickness of 65 feet. They are followed by 

 the Kiowa shales, with Gryphsea corrugata, which have been found to ex- 

 tend northward into southern Colorado, where they overlie the Morrison 

 formation, f It is not impossible that this horizon or a somewhat higher 

 one will be traced north as far as the Black hills, where a thin limestone 

 band holds the proper position. As will presently appear, only the lowest 

 Washita beds are deposited over this more northern area, the Dakota 

 regression beginning in early Washita, if not actually at the beginning of 

 Washita time, and continuing throughout that epoch. 



The West Coast transgression. — Marine Mesozoics are found in various 

 parts of the Pacific coast province of North America. The series begins, 

 as far as we know, with Lower Triassie, though the lowest Triassic (lower 

 Brahminic) has not yet been found. In the Meekoceras beds of the Aspen 

 Mountain, upper Brahmanic and lower Jakutic horizons are known, the 

 former (with Meekoceras, Aspidites, Pseudosageceras, Ophiceras, Propty- 

 chites, etcetera) occupying the lower 700 feet and resting upon Carbonic 



* Prosser : Geological Survey of Kansas, vol. ii, p. 96. 

 t Stanton : Science, n. s., vol. xxii, p. 756. 



