MESOZOIC TIME — CRETACEOUS. 819 



couver and Queen Charlotte Islands is referred to the Lower Cretaceous. 

 On Queen Charlotte Islands, fossil plants of Lower Cretaceous species occur 

 in the beds, as first discovered in 1872, and reported in the following year 

 by Dawson. G. M. Dawson makes five subdivisions of the beds ; and the 

 three lower, C, D, E, 9500 feet thick, are now regarded as identical with the 

 Shasta group, on the basis of several common fossils (Whiteaves, C. A. 

 White, T. W. Stanton). 



Arctic Ocean. — On western Greenland, in the vicinity of Disco Island, 

 there are deposits containing Cretaceous and Tertiary plants, and the lower 

 part are the Kome group, of Heer (1882), referred by him to the Neocomian 

 of Europe, and by Newberry and Fontaine to the age of the Kootanie 

 and Potomac. 



A portion of the Potomac formation in Maryland was referred, on account of its 

 stumps of Cycads, in 1860, by P. T. Tyson to the " Wealden" ; and in 1875 to the same 

 by W. B. Rogers. A careful study of the many fossil plants led Fontaine (1889) to essen- 

 tially the same conclusion. The remains of Reptiles which it has afforded (see beyond) 

 are pronounced Jurassic by Marsh. 



The Potomac formation in the region of the Chesapeake Bay, in Maryland, is described 

 by N. H. Darton (1893) as overlaid by beds of white sand, gravels, and brownish sand- 

 stones, which he calls the Magothy formation. It contains lignite and plant remains ; but 

 no fossils are mentioned for identifying or distinguishing it ; and its separation from the 

 Potomac by a plane of erosion is of uncertain importance. The Alhirupean group of 

 Uhler (1888) consists chiefly of white sand-beds occurring along the Chesapeake Bay, 

 and is largely exposed near the head of Magothy River ; and it is supposed to belong in 

 part with the Potomac formation. But such evidence is very doubtful; for the deposits 

 of sand, mud, and gravel now forming about Chesapeake and Delaware bays, and elsewhere 

 along the Atlantic border, show that kinds of material, color, coarseness, texture, struct- 

 ure, are nearly valueless characters for determining the equivalency of Cretaceous and 

 later-time beds as well as those of earlier time. All sorts are formed cotemporaneously, 

 and the same sorts at successive epochs. 



On the Gulf border, the Tuscaloosa group in Alabama, as described by Smith and 

 Johnson, consists of clayey layers with intercalated beds of sand ; it outcroi^s beneath and 

 either side of Tuscaloosa, along the northern limit of the Cretaceous belt. The thickness 

 is about 1000'. The Eutaw beds of Mississippi, first described by E. W. Hilgard, are 

 referred to the group, as far as non-marine, by C. A. White. The Tuscaloosa group is 

 described in detail by E. A. Smith and L. C. Johnson, in Bulletin 43, U. 8. Geul. Siirv., 

 1887, and some observations are added on the Eutaw group in Mississippi. 



In Texas, the Lower Cretaceous has a thickness to the northeastward, at Red River, 

 of 1000' ; to the southwestward, on the Rio Grande, of 5000' ; and northwestward it extends 

 into New Mexico. At Kent, 163 miles east of El Paso, the westernmost station in Texas, 

 the thickness is made about 600' by Dumble and Cummins; 550' of it belong to the 

 Washita division, and are characterized by the Gryphma dilatata var. Tucumcari of Mar- 

 cou, a fossil well known from the Cretaceous of New Mexico. In Kansas, the whole 

 thickness is but 150', half of it Trinity sands, and the rest, the Fredericksburg beds 

 (Cragin). 



The more important older investigations in Texan geology are those of Ferdinand 

 Roemer (18-52), B. F. Shumard (1856-1860), Marcou (1854-1859). Shumard made the 

 Washita and Comanche Peak groups Upper Cretaceous ; and Marcou placed the upper 

 line of the Lower Cretaceous between these two groups, with the Comanche Peak lime- 

 stone above. 



