g 



On the Silurian Basin of Middle Tennessee. 353 



5. Along the western side, the upper part of the second, the 

 whole of the third, fourth, and fifth groups crop out on the hill- 

 sides or bhifls forming the walls of the basin. Group Ihirdj 

 which is seen only along the western side, in sections, thickens 

 as we proceed south-westward, and emerging in the counties of 

 Perry-j Wayne, Hardin, &c., from beneath the superior groups, 

 which separate our basin from the bottom-lands of the Tennes- 

 see, becomes the surface-rock of these lands and the knobs alon^ 

 the river. On the south-eastern side of the basin, the slopes, 

 buiffs, &c., present sections corresponding to those of the oppo- 

 site side, with the exception of the entire absence of group i/nrd, 

 or the gray limestones of the Harpeth and Tennessee rivers. 

 (See section, on the map.) 



6. The uppermost group, including all above the black slate, 

 spreads out into a broad zone encircling the basin on all sides. 

 It thus forms the "Barrens" and flat lands lying along and in 

 front of the western slope of the Cumberland Mountains; run- 

 pnig eastward it disappears beneath the Pentremilal strata form- 

 ing their base. (See map.) From the mountains, the zone sweeps 

 off in a north-westerly, and then westerly course, through North- 

 Tennessee and Southern Kentucky, presenting us again with 

 barrens and flat lands. Tn this region, the Cany fork and Cnm- 

 herland river, intersecting the strata deeply, have cut out for 

 themselves narrow valleys, remarkable for their depth, their pre- 

 cipitous bluffs, and the beautiful waterfalls of their tributaries. 

 Bluffs five and six hundred feet high have been reported. 



The zone disappears in Kentucky, under the limestone slopes 

 of the Illinois coal-field. From this region, it extends, rich in 

 oxyd of iron, south through Tennessee, running under the creta- 

 ceous rocks west of the Tennessee river. The latter river and 

 Its tributary, the Duck, have here intersected the two topmost 



The zone com- 

 in North Alabama, 



groups and exposed (^5,) the limestones belo 

 pletes the circle, by sweeping off to the east 

 ^iHil it again reaches the mountains. 



7'. The groups and their members will be noticed in the as- 

 cending order, commencing with the lowest, as follows: 



V. Siliceous Group, \ ^-^^.^''"^ Mmesioue. 



^' \ a — Siliceous beds. , 



^^. Black or bituminous slate. 



ni. Harpeth and Tennessee River or gray limestone. 



c — Upper Nashville beds. 

 n. Nashville Group, \ 6— Lower Nashville beds. 



a— Siliceous, or sandy limestone. 



c Upper Lebanon limestone. 



1- Stones River Group, \ 6— Lower Lebanon limestone. 



a — Stones River beds. 



