1865.] 49 [Lesley. 



XII. Conglomerate Sandrock. 

 XI. Sub-conglomerate, or Lowest Coal Measures. 

 XI. Sub-carboniferous Limestone. 

 X. Upper Devonian (Catskill) White Sandstone. 

 IX. Upper Devonian Red Sandstone and Shales. 

 VIII. Middle Devonian (Chemung) Clay Sandstones. 

 VIII. Lower Devonian (Portage, Hamilton, and Upper 

 Helderberg) Olive Shales and Black Slates, viz.: 

 Genesee Slate; 

 Tully Limestone; 

 Hamilton Slate; 

 Marcellus Shale; 



Corniferous and Onondaga Limestone; 

 Scoharie Grit; 

 Cauda-galli Grit. 

 VII. Oriskany Sandstone. 



VI. Upper Silurian (Lower Helderberg) Limestones: 

 Onondaga Salt Group ; 

 Gait Group; 

 Niagara Group. 

 V, IV, III, II, I, it is not needful here to specify. 

 Enough has been said, perhaps, respecting the Conglom- 

 erate ; and respecting the No. XI Ore and coal-shale system 

 under it. 



No. XI Limestone is the next Important formation to con- 

 sider. Just the reverse of No. XII, and the other sandstone 

 formations, which have their greatest thickness along the At- 

 lantic seaboard, this "Sub-carboniferous Limestone" of the 

 Great West tlmis away easUvard (or northeastward) almost 

 to nothing ; is scarcely 10 feet thick where it enters Mary- 

 land, and not 2 feet thick in Eastern Pennsylvania. But in 

 Southern Virginia it is quite large ; and in Middle Kentucky 

 it is twice as thick as No. XII, but, like it, subject to great 

 variations. Only 70 feet thick on Tygert's Creek in Greenup 

 County on the Ohio River, it increases to 400 feet in Clin- 

 ton County on the Tennessee State line. It is composed of 

 alternating white, gray, and buff-colored layers of rock, vary- 

 ing in quality from the most argillaceous claystone to the 



VOL. X. — G 



