MINERALOGY OF THE PENTLAND HILLS. 187 



The very small granular varieties of this rock, 

 which are principally composed of felspar and 

 quartZj are very nearly allied to the grey-wacke 

 of this district ; indeed, in some instanced, it is 

 difficult to distinguish the one from the other in 

 single specimens ^. 



This fact, in conjunction with one about to be 

 mentioned, namely, That clay-slate occurs in con- 

 glomerate, goes to support an opinion I have long 

 entertained, that Transition rocks may alternate 

 with the oldest Floetz rocks ; and, therefore, that 

 the rocks of the transition and the floetz classes 

 are not separated from each other in the manner 

 generally alleged by mineralogists. 



The conglomerate is sometimes very small gra- 

 nular, and earthy in its appearance, and then it is 

 compact, and, both externally and internally, is not 

 unlike certain varieties of basalt and Vv^acke. Va- 

 rieties of this kind occur at the base of Turn- 

 house Hill, also at Kirk Hill, and in the lower 

 part of the West March Burn. It is distinctly 

 stratified, and coarse and fine granular strata alter- 

 nate with each other. The strata are in general 

 inclined at angles from lO** to 30°. Thin lay- 

 ers of a variety of greenish-grey coloured clay- 

 slate occur in it. 



* If the Grey-wacke of the Pentlands is a chemical deposite, 

 the same must be the ease with the Conglomerate rock d«scribe4 

 in the text. 



