Page:Transactions of the Geological Society, 1st series, vol. 3.djvu/175



E. Mulattoe or Green Sandstone.

To the general account of this rock given in the Introduction, it may be added, that on treating different specimens with acids they were found to contain about nine-tenths of calcareous matter, the residuum consisting of green chloritic grains, mixed with quartzose sand or gravel.

The mulattoe is seen in Colin glen, a valley on the south-west of Divis hill near Belfast, and in several other places on the slope of that mountain; it is evidently interposed between the slate clay of the lias formation and the chalk. It occurs also at Cermoney, about five miles north-east from Divis, The chloritic grains in the mulattoe of Divis are small and very numerous, the calcareous base greyish and compact; it is traversed by slender veins of calcareous spar: besides the smaller grains of quartz, it contains a few larger pebbles with a reddish tinge.

Since it is not quarried for any economical purpose, we have no opportunity of ascertaining accurately the thickness or extent of the bed.

It is seen however near Larne, and considerably further north near Gerron point, occupying a position corresponding to that in which it occurs near Belfast, and it seems highly probable that it extends beneath the chalk throughout the intervals separating these points; indeed I am inclined to believe that where the series approaches to completeness, this member will seldom be found wanting.

In Murloch bay, where the line of chalk commences on the cast of the greenstone mass of Fairhead, a thin seam of quartzose pebbles cemented by green sand, affords traces of this formation; it separates the chalk from a thick bed of red sand.