224 James Neihon — Old Red and Carboniferous of Arran. 



thick sandstones which overlie the upper limestones near the Cock of 

 Arran, appears to be wanting. 



I will, therefore, take up the strata on the north coast, at the point 

 half a mile north of the shepherd's house at Laggan. This part is 

 generally called Salt Pans. These consist of sandstones and shales, 

 with two or three seams of coal, which have been wrought down to 

 the level of the sea; also several ironstones, three bands of which, 

 exposed in a little bay, have long been noted for their beautifully 

 tessellated structure. 1 



No marine remains have been recorded, nor observed by me from 

 these strata, the beds presenting the appearance of having been de- 

 posited in fresh water. They contain numerous plant-remains, mostly 

 indecipherable, although Stigmaria is common, and I found a small 

 frond of Sphenopteris. Dr. Bryce says (p. 128) that '■ the shale and 

 coal tract is bounded by a black limestone below and a red limestone 

 above, 1400 yards apart." These lie between the Lower and the 

 Upper Limestone series, and I believe they are the representatives of 

 what are denominated in the West of Scotland " the Middle Coal 

 and Ironstone series." These are represented in the neighbourhood 

 of Glasgow by the Possil and Govan Coals and Ironstones, with 

 which they correspond in geological position, mineral character, and 

 economic products of coal and ironstone, although we have not 

 observed the Lingula, which is so characteristic of this division. 



Proceeding still north-west along the shore, we find overling 

 the last group another series of red rocks, even redder than before. 

 These consist of sandstones, shales, and several limestones. The 

 limestones are charged with marine fossils ; one bed (the lowest) 

 being covered with shells of Productus latissimus, 2 while another 

 abounds with large stems of encrinites, and a third with various 

 shells. Not only these beds, but the fossils they contain are as red 

 as any Old Eed Sandstone rock in Scotland. These beds exhibit 

 a decided change from the last group, viz. a change from fresh- 

 water to marine conditions. 



I consider these beds to belong to the Upper Limestone series, 

 to which they correspond in stratigraphical position. Productus 

 latissimus attains its greatest development at a certain horizon 

 known in the West of Scotland as the Productus latissimus limestone, 

 also as the Index or Cowglen limestone, which is the lowest lime- 

 stone in the Upper Limestone series ; and I am inclined to consider 

 the Arran bed charged with Productus latissimus to be the Index 

 Limestone itself. 



Overlying these rocks at the Cock of Arran are thick beds of 

 sandstone, then breccias, then sandstones again, till the whole are cut 

 off by a great fault and by the slates coming down to the shore. It 

 will be observed that these sandstones occupy the natural position 

 of the Millstone Grit, and as no unconformity or break in the 



1 This bed is referred to by Mr. E. A. Wunsch in a paper, " On a Coast Section 

 at Arran," read before tbe Geological Society of Glasgow, March 2nd, 1871 : Geol. 

 Mag. 1871, Vol. VIII, p. 2R6. 



2 See Mr. E. A. "Wunsch' s paper already referred to. 



