380 ARRAN. GEOLOGY. SECONDARY STRAJTA. 



of the limestone vary in different parts, but its colour 

 is generally a dark purplish grey. It is often very impure, 

 being much mixed with clay and siliceous earth ; particu- 

 larly at the surfaces of the beds, where it generally passes 

 gradually into the marie. It is at times of a conchoidal OF 

 flat and smooth fracture, at others granular, with a grain 

 more or less large. These beds, whether calcareous or 

 argillaceous, contain various entire shells, together with 

 fragments of the same bodies, and specimens that appear 

 to have lost their original forms by pressure. The nature 

 of many of these fragments, and of the compressed and 

 distorted shells, cannot be ascertained, but some of the 

 latter seem to have been pectines. The only entire shells 

 which I observed were two species of terebratula, and 

 I am not aware that those who have made mineral con- 

 chology their study have yet assigned specific names to 

 them. It is rare to find the individuals, in the rocks 

 of this era, sufficiently perfect to exhibit those minute 

 circumstances of structure on which specific distinctions 

 are founded. Besides these shells, some of the beds con- 

 tain madreporites* 



The preceding description comprehends only one set 

 of these beds, being that wrought in the oldest quarry ; 

 but there are similar alternations in other places, which it 

 is unnecessary to specify, as they are but repetitions of 

 the former. It is proper here to remark that these strata 

 are not only inclined to the south-east, or thereabout, 

 conformably to the general position on this side of Scri- 

 den, but that the angle is here considerable, the quarries 

 being situated in the hill. At the same time, the large 

 shells are all placed with their convex surfaces towards 

 the bottom of the stratum ; a circumstance well known 

 to be common in similar .cases. 



Proceeding further southward, a frequent alternation is 

 seen between the red and white sandstone, for a con- 

 siderable space ; until at length the former takes exclusive 

 possession of the ground, continuing to Screeb. Here 



