104 PROCEEDINGS OF SOCIETIES. 



which explain and accompany it, are not borne out by the facts, as I shall 

 endeavour to show. The geological phenomena which are visible in the 

 counties of Cavan, Fermanagh, Leitrim, and Sligo, may be interpreted, 

 without any difficulty, by means of the three members of the Carboni- 

 ferous formation set forth in No. 1, the Old Red Sandstone, Mountain 

 Limestone, and Coal Rocks ; and these afford a reference for every rock 

 in the localities, described in the most simple manner. 



In proceeding to show my reasons for the statements I have made, 

 and my views on the subject generally, I shall notice the quotations 

 from the " Outline" as nearly in consecutive order as I can. 



In quotation No. 1, the author says : — " The secondary rocks are di- 

 vided into Old Red Sandstone, Carboniferous Limestone, and Coal, and 

 its accompanying strata." 



It is remarkable that the Carboniferous Slate, that is, a slaty band 

 which lies between the Old Red Sandstone and the Limestone, has not 

 been noticed at all in this " Outline." Mr. Griffith subsequently intro- 

 duced this member into his classification, as shown upon his recent 

 Maps, and it is a good and true member. It is well developed on the 

 shore at Poulscadden, near Howth ; also on the shore near the Martello 

 Tower at Portmarnock, in the county of Dublin ; and many other parts 

 of Ireland. With this subdivision, the natural succession in the Carbo- 

 niferous formation is — 



1. Old Red Sandstone. 



2. Carboniferous slate. 



3. Limestone. 



4. The Coal series. 



Each of those subdivisions is composed of a different mineral sub- 

 stance from the others. The bulk of the Old Red Sandstone is composed 

 of red sand ; the Limestone of lime ; and the Coal shales of argillaceous 

 or clayey matter. There are, however, modifications in the subdivisions 

 which require some explanation, into which I shall enter in detail as I 

 proceed. 



Athough those subdivisions differ so widely from each other in mi- 

 neral character, yet, as a whole, the system exhibits the remarkable cir- 

 cumstances : — 1. That the beds of which it is composed are parallel to 

 one another. 2. That they rest unconformably on the inferior or under- 

 lying rock. 3. That they are covered unconformably by the superior 

 or overlying rock. 4. That this parallelism of the strata clearly points 

 to one great geological epoch, in which the whole suite, from beginning 

 to end, was deposited, without any great catastrophe in the succession. 



The Old Red Sandstone is the lowest of those subdivisions. It may it- 

 self be divided into three parts : — First, or bottom layer. Red conglome- 

 rate, composed of rounded pebbles of white quartz, brown quartz, jasper, 

 and fragments of other rocks, united by a mineral paste. In some lo- 

 calities the conglomerate is composed of flattish, rounded stones of mica 

 slate, as at Cushendall, in Antrim ; sometimes of green chloritic slate, 

 or green grit, as at Lane, and at Shenick Island, near Skerries, in Dublin. 



