820 HISTORICAL GEOLOGY. 



The Lower Cretaceous of northern Mexico, in Chihuahua and Coahuila, was described 

 by C. A. White in 1889, who speaks of the strata of bluish limestones as strongly upturned 

 and flexed, and having a thickness in the Sierra San Carlos of 4000'. Felix and Lenk, in 

 their memoir of 1890, 1891, separate from the Cretaceous of Texas a lower part, consisting 

 of gray to black limestones having intercalated clays as the Lower Cretaceous, and refer 

 the rest, which consists chiefly of whitish, somewhat cherty limestones, to the Upper. He 

 reports the former as having nearly three fourths of its 46 species of described fossils 

 identical with the Neocomian of Europe ; and the latter as containing Radiolite-like forms, 

 with species of Caprina and Nerinea. 



The Kootanie beds of Montana, which in some places contain beds of coal 12' thick, 

 were described by Newberry in 1887, and by H. Weed in 1872. 



The Knoxville and Horsetown beds, i.e. the Shasta portion of the Shasta-Chico series, 

 have a wide distribution along the Pacific coast, extending with interruptions from south- 

 ern California probably to Alaska. Their greatest development, according to Diller, is 

 upon the western border of the Sacramento valley of California, where they are composed 

 chiefly of shales with only occasional sandstones above and many thin beds below. The 

 beds are rarely calcareous, and where the successively newer overlapping series come in, 

 lying unconformably on the pre-Cretaceous metamorphic rocks, local conglomerates are 

 common. The greatest thickness of the Knoxville beds measured is nearly 20,000'. The 

 absence of faults is not assured. The Horsetown beds have a thickness of over 6000', and 

 overlap the Knoxville beds in all directions toward the Cretaceous shore. The conforma- 

 bility of the Knoxville and Horsetown beds and their detrital and faunal continuity in 

 both California and Oregon indicate uninterrupted sedimentation ; and the shoreward 

 overlapping of the newer beds, with marked unconformity upon the pre-Cretaceous rocks, 

 shows that upon the Pacific border the land was subsiding and the sea encroaching. 



2. Upper Cretaceous. 

 Atlantic Border. 



On the Atlantic border the Upper Cretaceous formation outcrops from 

 Martha's Vineyard, along the islands south of ISTew England to New Jersey ; 

 thence it continues southward, in a narrow belt by the west side of the 

 Tertiary to southern Virginia. It occurs in North and South Carolina only 

 in small patches. Near Macon, Ga., a belt commences north of the Tertiary 

 area, which widens westward, and, on approaching the Mississippi valley, 

 spreads northward up its east side to the Ohio near Paducah ; where it 

 crosses the river and narrows out in an area of sandy clays and "micaceous 

 sands " like those of the Kentucky Cretaceous beds. The rest of the Missis- 

 sippi Bay of the Cretaceous Period became covered later by Tertiary beds and 

 fluvial deposits. 



The formation along the New Jersey coast includes at bottom a fresh- 

 water group, called the Earitan, and, above this, beds of greensand or marl 

 interstratified with beds of common sand, clay, and occasionally of marine 

 shells. Remains of Reptiles are sometimes found in the upper beds, and 

 occasionally a complete skeleton. 



The subdivisions as laid down by G. H. Cook are given in the following 

 table ; and the epochs to which they probably belong are also stated. 



