148 Dr. Berger on the Geological Features 



The limestone itself somewhat varies in its characters at the 

 diflerent places where it occurs. In point of colour it passes from 

 bluish-black to smoke-grey : the first variety is more compact, the 

 lamellar concretions less evident, and it is sometimes traversed by 

 veins of flinty slate ; small quartz concretions are occasionally though 

 rarely interspersed in it. I have seen in it crystallized iron pyrites : 

 it contains superficial impressions of cornua ammonis, covered with 

 iron pyrites; madrepores, both ramose and columnar; nautili figured 

 by Walcott, (Bath fossils fig. 44.) 



Two small limestone districts occur near the shores of Strangford, 

 Lough, one at Lisbawn near Down Patrick on the south-west, and 

 the other near Cumber on the north-west ; the latter appears to 

 be of the magnesian variety ; orthoceratites have been noticed in it. 



It has not been ascertained to what formation these limestones 

 belong, but since they occur in a district where greywacke prevails, 

 they may with greater propriety be noticed here than under any 

 other article. 



C. Transition Trap, 



The formation of greenstone which alternates with the limestone 

 at Carlingford has invariably a crystalline texture, but differs in its 

 other characters in presenting the following varieties, 



1. Common greenstone. 



2. Close grained and porphyritic. 



3. Approaching to greystone. 



The beds are three or four feet thick. 



