APPENDIX D. GEOLOGY. 157 



characteristic species : Archimedipora archimides, Agassizocrinus dacty- 

 liformis, Pentatematites sulcatus, Productus cora, P. punctatus, P. cos- 

 tatus, Terebratula subtilita, and Terebratula Marcyi* We have found 

 all these species associated together in Grayson county, Kentucky, near 

 Salem, Indiana, and at Chester and Kaskaskia, Illinois. 



The line of junction between the sandstone and limestone is well 

 defined, there being an abrupt transition from the one into the other. 

 The sandstone has yielded but few fossils, and these only calamites and 

 ferns. 



Veins of sulphuret of lead traverse the limestone at several points 

 in Washington county, and I have been informed that valuable beds of 

 iron ore occur here ; workable seams of bituminous coal have also been 

 discovered at a number of localities in the county. 



Proceeding in a southerly direction through the counties of Crawford 

 and Sebastian, the limestone, which, with few exceptions, constitutes the 

 surface-rock in Washington county, dips beneath the sandstone, and 

 the latter forms the entire mass of the hills, rising sometimes to the 

 altitude of a thousand feet above the adjacent streams : it is, for the 

 most part, the prevailing rock the entire distance between Fort Smith 

 and Camp Belknap. The sandstone is often highly ferruginous, and 

 varies in color from light-gray to dark brown. It exists in heavy mas- 

 sive beds, made up of coarse quartzose grains, with intercalations of 

 finer-grained sandstone, occasionally beautifully ripple-marked. It cor- 

 responds in its lithological features with that forming the Ozark range 

 of mountains. 



In Sebastian county I found a few Calamites, Lepidodendra, and 

 several varieties of fossil ferns of the coal formation, but organic remains 

 are by no means abundant. Bituminous coal exists in almost inexhaust- 

 ible quantities throughout the county. The seams vaiy in thickness from 

 a few inches to seven feet, and they lie in such a manner that they can 

 be wrought easily. Coal has also been discovered at a number of local- 

 ities between Fort Smith and Fort Washita. 



About a hundred miles southwest of Fort Smith we encountered an 

 outcrop of bluish-gray limestone, which extends across the country in 

 a southeasterly direction for the distance of about twenty miles; it 

 presents an average thickness of about ten feet, with a dip to the east of 

 30°. Its precise character could not be determined, as we were unable 

 to find any fossils. 



* Figures and descriptions of the fossils of these beds will bo found in the 

 appended report of Dr. B. F. Shumard on the pateontology of the expedition. 



