Page:Transactions of the Geological Society, 1st series, vol. 3.djvu/156



The limestone itself somewhat varies in its characters at the different 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 magnesia 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.