GEOLOGICAL SOCIETY OF DUBLIN. 125 



band below the gray limestone of Dublin, which comes to the surface 

 in many places. From Portmarnock to Malahide, on the sea-shore, is 

 an excellent typical section of this band. 



The upper or millstone grit band is seen in the railway cutting near 

 Malahide, at the second viaduct south of the town, adjoining the demesne. 

 About forty yards to the north of this viaduct there is a fault, visible in 

 the cutting, on the north side of which is gray, hard limestone ; on the 

 south, black, soft shale (now called Calp), belonging to the coal shales. 

 From the angle of the slope of this fault the geologist will infer that 

 the black rock slipped down from a higher level. Here an instructive 

 comparison may be made between the Carboniferous Slate at Portmarnock 

 Martello Tower and the black shale at the viaduct. The rocks at this 

 break are unconformable, for they dip nearly in opposite directions from 

 the line of fracture. The Carboniferous Slate at the Tower contains beds of 

 crystalline encrinital limestone, amounting in volume to about half the 

 mass. The shale (Calp) at the viaduct has no limestone beds at all — 

 not, I suppose, an ounce in a thousand tons of the mass. The contrast in 

 fossils is this, that out of the 1050 species, exclusive of plants, got in the 

 Carboniferous formations, the Carboniferous Slate contains nearly all the 

 shells and corals found fossil in the limestone ; while the shales above 

 contain only from 3 to 4 per cent, of the entire number of the shells, and 

 none at all of the corals. 



I have just said that the coal shales contain about 3 or 4 per cent, 

 of the fossils common to the limestone. This makes a pretty large 

 number. I stated before, that there were but very few species common 

 to the two. To explain this apparent discrepancy I will state, that in 

 a ravine at Cahernanalt, two miles north-east of Keadue, in Roscommon, 

 and about 150 feet above a bed of coal, I found a bed of black, calca- 

 reous shaly rock, about three feet thick, and in it I got a bag of fossils. 

 These were examined by Mr. M'Coy, and he stated that out of 35 species 

 obtained, 26 were common to the mountain limestone, and 9 either 

 peculiar to the coal shales or new. I would enumerate them here ; but 

 my paper is getting long, and I may make them the subject of a future 

 communication to this Society. 



While on this point, I will further add, that those fossils found high 

 up in the coal rocks, and the fossils before enumerated, found below in 

 the Old Red Sandstone, which are in both cases common with those of 

 the middle part (the limestone), show two strong links, made by nature, 

 connecting the coal rocks, the limestone, and the Old Red Sandstone 

 with one another into one formation inseparably, and putting them in 

 the position in which they were placed by geologists about the year 

 1835. 



If the rock called Calp of the Dublin district were a band made up of 

 shale and sandstone, between two limestones, as represented in quotation 

 No. 4, the Upper Limestone might be expected to appear in some part 

 of this extensive district overlying the Calp band ; but no limestone 

 exists over this peculiar black shale anywhere in Dublin, Meath, or 

 "Westmeath. I have no doubt whatever that this whole district, coloured 



