Horizon of Dr. Scolders Dithyrocaris. 277 



Limestone is simply a phase characteristic of the top of the Blackbyre 

 Limestone, and as the top of the limestone is not seen at the type 

 locality it is quite possible that it may be present though not exposed. 



The section exposed at Jenny's Well, a quarter of a mile to the 

 east of Blackhall, Paisley, is practically a counterpart of that seen in 

 the Arkleston Catting, and the additional corroborative evidence 

 bearing upon the relationship of the Gallowhill Limestone to the 

 Blackbyre Limestone is so complete that it requires to be examined 

 in some detail. The section shows a fairly continuous sequence from 

 the Blackhall Limestone down to the base of the sill of dolerite which 

 here occupies exactly the same stratigraphical position as in the 

 Arkleston Cutting, having the Hurlet Limestone above and the 

 Blackbyre Limestone below. 



Unfortunately the outcrop of the Blackbyre Limestone cannot be 

 seen, but its position is shown by a hollow immediately to the west 

 of the dolerite sill, which runs in a north and south direction from 

 the Cart up the side of Dykebar Hill, marking the line along which 

 it was formerly quarried. Just at the point where the road crosses 

 the railway the Blackbyre Limestone was exposed during the making 

 of the line. It cannot now be seen, but the walls on each side of the 

 railway at this point are built of it, and the blocks of limestone show 

 all the features of the Gallowhill Limestone on the one hand and of 

 the Blackbyre Limestone of the type section on the other. 1 



An examination of the exposure of the Blackbyre Limestone seen 

 in the bed of the Levern at Neilston, a little above the point where 

 it crosses the main road to Lugton, helps, we think, to throw some 

 light upon the relationship of the Gallowhill Limestone to the 

 Blackbyre Limestone. The section here is somewhat obscure, but 

 the main mass of the limestone is rich in corals and Productidse. The 

 former are represented by bands of Lithostrotion and solitary corals, 

 the latter by various species of Productus and by numerous specimens 

 of the large variety of Productus giganteus. On the top of the main 

 mass of the limestone rests a bed of fine-grained cementstone, which 

 presents all the features of the Gallowhill Limestone. Traced into 

 North Ayrshire, it forms the peculiar fine-grained top of the Dockra 

 Limestone and its equivalents, which we have elseAvhere shown to be 

 the same as the Blackbyre Limestone of the Hurlet section. 



An examination of the sections exposed in the burn at Meikle 

 Corseford, and on the Gryffe Water below Bridge of Weir, also 

 affords certain evidence which goes to confirm the relationship of the 

 Gallowhill Limestone to the Blackbyre Limestone. At both localities 

 the Blackbyre Limestone is capped by a fine-grained crinoidal lime- 

 stone comparable to the crinoidal phase of the Gallowhill Limestone. 

 A.nd at both these localities it is overlaid by the peculiar green ashy 

 mud which is probably identical with the so-called fuller's earth 

 found in the Gallowhill Quarry. 



1 The evidence derived from these blocks shows that the Blackbyre Lime- 

 stone of this locality has a strong resemblance to that exposed in the Beith 

 Quarries. It carries a varied Brachiopod fauna and contains thick bands of 

 Lithostrotion and other corals. 



