TUURPHREE'S VALLEY; GEOLOGICAL FORMATIONS. 17 



the geological structure, will be more clearly presented in 

 the progress of its structural description. It will be under- 

 stood from what has been stated that all of the sub-valleys 

 described, with the intervening marginal ridges, make up 

 and constitute Murphree's Valley. That it is environed by 

 Ooal Measures, except on the south-west end ; and that these 

 measures adjoin or abut against the valley in an elevated 

 rim on both sides. 



GEOLOGICAL FORMATIONS. 



On a preceding page we have given a table of the Geolog- 

 ical Formations exposed in Murphree's Valley. It is nec- 

 essary, for the proper understanding of much that follows, 

 that we should now describe these formations in some detail. 

 In this description they are considered in descending order: 



CARBONIFEROUS. 

 1. Coal Measures. 



The coal measures cover the surface on both sides of this 

 valley. On the north-west side they are thin, rarely exceed- 

 ing 100 feet at the edge. Only the base rocks have been 

 left. The lower conglomerate is generally the crest of the 

 valley rim. On a portion of the opposite side these measures 

 are known to be over 2,000 feet thick. Nearly this depth of 

 strata has therefore been washed away from the top of the 

 north-western rim. The measures, however, rapidly deepen 

 towards the north-west. The dip of the strata in that direc- 

 tion is about 15. The lower conglomerate rock here, as 

 elsewhere, is from 80 to 100 feet thick. In its lower part it 

 is often strictly conglomerate, wholly composed of pebbles, 

 firmly cemented together with silica, or silica and iron. 



