"98 PROCEEDINGS OF THE CANADIAN INSTITUTE. 



the power of transporting. In other words, whenever the transport- 

 ing agent becomes so that it is unable to carry off the amount of 

 detritus provided by the disintegrating force, then weathering will 

 accommodate itself to the transportation by the accumvUatioii of 

 detritus bringing the action of weathering to a balance. Wlienever 

 this equilibrium is established, erosion will proceed at a uniform rate 

 depending entirely upon the nature of the material to be eroded. 



The rocks forming the bottom of the Central Basin consist of the 

 comparatively soft argillaceous thin bedded rocks of the Trenton and 

 Nashville, easily weathering upon exposure to atmospheric agencies. 

 In many places rounded knob-like hills rise up about 100 or 150 feet 

 above the general level of the plain. These knobs consist of thin 

 bedded light blue argillaceous limestones, and are in some cases 

 absolutely devoid of any detritus ; in others there is a scanty partial 

 covering of gravelly material. Generally though, these knobs have a 

 somewhat slight covering of gravelly soil out of which a stunted 

 growth of cedar is found growing. 



Along the streams at the foot of the knob there is usually a small 

 extent of bottom land varying with the size of the creek, but none of 

 any very great extent except where the creeks flow into the river. 

 Along the banks of the rivei-s, particularly the Cumberland, there are 

 extensive tracts of this bottom land made up of the detritus brought 

 down from the higher grounds by the action of the streams. 



The beds of the various creeks flowing from the escarpment are 

 generally composed of gravel of a rusty brown or orange color, and 

 containing fragments of fossils belonging to the beds through which 

 they have cut a passage. In every case the streams have worn and 

 rounded the rock bedding in the sides and bottoms. Even the small- 

 est seem to have a considerable eflect. 



In the various railroad cuttings the exposures of rock are 

 weathered to a considerable extent. Near the southern end of the 

 Cherry Street Station there is a cutting shewing three beds of thick, 



