so PROCKEDINGS OF THE CANADIAN INSTITUTE. 



From the rlistribiition of the Lower Helderberg rocks it is appar- 

 ent that the area under consideration was still dry land, and even had 

 during the Niagara period been increasing in elevation. But while 

 this elevation was in process there must also have been some denuda- 

 tion. The top of the Hudson River dome was exposed to the action 

 of the waves as well as aerial conditions during the long period which 

 was occupied in building the Niagara and Lower Helderbei-g formaiions 

 and at least the whole of the Niagara and a great part of the Helderberg 

 ■were built out of the debris of the Hudson River or Nashville rocks, 

 forming the territory, part of which now forms the Central Basin. 



West of the Tennessee, the palaeozoic formations terminate in an 

 abru])t and bi-oken off manner, as if they had been subject to fracture 

 and afterwards to an erosive action similar to that undei'gone by a 

 rocky coast line under the influence of wave action. They form an 

 ■escarpment against which the newer bed.s of the Cretaceous abdt at a 

 considerably high angle. 



This breaking off or termination of the Palaeozoic rocks follows 

 approximately the course of the Tennessee River valley across the 

 States of Tennessee and Kentucky, but with the exception of only a 

 short distance of about 18 miles in Harding County, Tennessee, the 

 old escarpment formed by the break is not coincident with the course 

 of the river but passes along to the west ; the Tennessee having cut a 

 channel out of the older foi-mations to the east. 



This old shore line, for it is in reality a shore of very ancient origin 

 and of lonof continuance, is broken in several places by long narrow 

 bays. The length which these bays have obtained and the position in 

 which they are placed indicate a long continued and at the same time 

 great difference in the drainage system of the country, at the time the 

 waves of the Silurian seas beat upon its beach or broke in 

 spray against the cliffs from what we now find it. The course of 

 the Tennessee River with its subordinate system of drainage has a 

 northward flow, but the old gorges or stream channels disclosed in the 

 palaeozoic shore line indicate a southern or south-western course for 

 the drainage of that time. Li Benton County a nari'ow strip of ere- 



