THE SOUTHEASTERN MESOZOIC DEPOSITS. 275 



Jurassic beds represented in northern New Mexico, although Marcou in his 

 earlier explorations, coming to the region from the east and along a line not 

 visited by either of the others, found beds corresponding to what he had 

 considered as Jurassic in northern Texas. Newberry found Triassic plants 

 in reddish sandstones immediately beneath sandstones which he regarded as 

 Cretaceous, but it does not appear from his published accounts that their 

 relative position was such as to preclude the possibility of a slight uncon- 

 formity lid ween them. 



Further south, in the Zufii mountains, Button found a considerable thick- 

 ness of sandstones above the " Red Beds" which he regarded as probable 

 representatives of the Jurassic of the Plateau region, although he obtained 

 no fossils from them. 



To the eastward, in the region around the southern end of the Sangre de 

 Cristo range, Stevenson found the Dakota Cretaceous to have suddenly 

 thickened to 1,700 feet from the normal development of about 300 feet 

 which obtains with remarkable regularity from a few miles northward along 

 the whole front of the Colorado range, and this thickening seems to have 

 taken place below the sandstone generally recognized as characteristic of 

 the Dakota throughout the Rocky Mountain region. He, also, failed to 

 recognize the Jurassic of Marcou. New-berry, however, thinks to have 

 recognized representatives of the fresh-water Jurassic in northern New 

 Mexico *. 



Texas and Arkansas. — Recent geological observations in Texas and west- 

 ern Arkansas show, according to Mr. R. T. HilLf that the marine Creta- 

 ceous beds of that region have been deposited along the southern base of an 

 uplift, as yet imperfectly known, of the Paheozoic rocks, extending from Ar- 

 kansas westward through Indian Territory and northern Texas, and south- 

 westward into New Mexico. It is not yet definitely known whether early 

 Mesozoic beds are involved in this uplift, so that its formation could be 

 correlated with the Jurassic movement in the Rocky Mountain region, 

 though certain facts render this probable. 



The Cretaceous beds are divided by Mr. Hill into an upper and lower 

 series, divided by a land epoch marking a physical as well as a palseontolog- 

 ical break. The upper beds deposited since this break show a similar cycle 

 in the character of their sediments with the Cretaceous beds of the Rocky 

 Mountains, with which they are correlated by Mr. Hill, the Lower Cross- 

 Timber (Dakota) being a littoral formation, with basal conglomerate and 

 abundant plant remains. The succeeding beds indicate gradually deepening 

 waters culminating in the Rocky Comfort chalk (Niobrara), and showing 

 evidence of a shallowing sea in the upper series, which corresponds to the 



*;Personal communication. 



t.\m. Jour. Sci., 3d ser., Vol. XXXVIII, 1889, p. 282. 



