THE COAL MEASURES OF ARKANSAS 36 1 



of the Missourian ; one-half of the number are found lower 

 down, and no less than seven are typical Des Moines forms, in 

 fact having an optimum habitat not in the marine beds but in the 

 bituminous shales. The seven species of glossophora that are 

 enumerated are the most abundant forms of the Lower Coal 

 Measures throughout the northern district, and they are pre- 

 eminently the characteristic fossils of the black shales every- 

 where. Among the ten cephalopods named, no less than five 

 are of common occurrence in the Des Moines beds, and not 

 infrequently they are found in the black shales ; the other five, 

 so far as known, range low in the Missourian. 



If the faunal evidence, as recently presented, is to be relied 

 upon at all, it would appear that there are no grounds for believ- 

 ing that there are necessarily present in the deposits of the 

 Arkansas valley region any strata higher than the base of the 

 Missourian series of Missouri and Kansas. 



There is, however, another reason for believing that no part 

 of the Missourian series, or its equivalent, exists in Arkansas. 

 The general stratigraphy as far as it is now understood, gives 

 not only no indication of the Missourian beds being repre- 

 sented in the region, but points almost conclusively to their 

 absence. 



The broad belt of lowland, lying below the contour of 

 IOOO feet, and between the Ozark uplift and the elevated 

 region of the Great Plains, extends from the Missouri river 

 southwestwardly into Indian Territory and then eastwardly 

 through the Arkansas valley to the savannas of the Missis- 

 sippi embayment. This lowland is occupied chiefly by shales 

 which have relatively much less resistant powers to erosion 

 than the limestones on either side of the belt. In Missouri the 

 subdivisions of the Coal Measures, both " Upper " and " Lower," 

 have been clearly made out. In Kansas Haworth z has traced 

 the same divisions to the Indian Territory line, so that down 

 to the juncture of the great lowland valley and that of the 

 Arkansas, the surface distribution of the several formations of 



I Univ. Geol. Surv. Kansas, Vol. I, 1896. 



