276 Notices of Memoirs — P. Macnair — 



to the west of the outcrop, as drawn on the map, is made clear both 

 from the evidence derived from the old quarry opposite the Mote Hill 

 and also from recent information that we have obtained which shows 

 that Gallowhill House rests upon it. But whether it is continuous 

 over this area or is repeated by faulting we have no data to decide, 

 and the position of the outcrop is left much as it is given in the 

 6-inch-to-the-mile Geological Survey map. 



The statement in the Statistical Account that the layer of till 

 immediately above the Gallowhill Limestone for several inches closely 

 resembles fuller's earth is of great interest, as we seem to recognize 

 in this the peculiar ashy fireclay which is generally found to rest on 

 the eroded top of the Blackbyre Limestone of Kenfrewshire and 

 North Ayrshire. 



In interpreting the structure of the ground between Arkleston and 

 the Cart it seems to us that there must be a low arch bringing in the 

 strata that lie immediately below the Hurlet Limestone. On the east 

 this arch sinks below the Hurlet Limestone, as exposed in the 

 Arkleston Cutting, and on the west it must pass below the outcrop 

 of the Hurlet Limestone and Coal which has been drawn by the 

 Survey to cross the White Cart Water near Carlisle Quay and 

 Nethercommon. An exposure of limestone underlaid by a bed of 

 coal with pyrites can at present be seen at low tide immediately 

 below the Swing Bridge at Carlisle Quay, but owing to the limited 

 nature of the exposure it is at present difficult to determine whether 

 this is the Hurlet Limestone or the Blackbyre Limestone, but it is 

 certainly the equivalent of one of these. 



Bores put down along the outcrop of the dolerite on the Gallowhill 

 Policies show that the dolerite rests along this line upon a series of 

 thick-hedded shales, fireclays, and sandstones which have been bored 

 into for a depth of more than 30 fathoms. There can scarcely be any 

 doubt that the uppermost of these represent the sediments which lie 

 between the Blackbyre Limestone above and the Hollybush Lime- 

 stone below. On the 6-inch-to-the-mile Geological Survey map 

 a bore put down to the south of Gallowhill shows the presence of 

 a coarse limestone 1 ft. 7 in. thick at a depth of 12 fathoms. This is 

 probably upon the position of the Hollybush Limestone. 



Comparison with the Blackbyre Limestone at other Localities. 



From the evidence that has been adduced there can be no doubt 

 that the Gallowhill Limestone must lie somewhere on the horizon of 

 the Blackbyre Limestone, and we now pass to consider the evidence 

 that exists bearing upon the lithological and palaeontological charac- 

 teristics of the Blackbyre Limestone in this district. At the type 

 locality (Blackbyre Farm) the Blackbyre Limestone consists of two 

 parts, a, lower full of small Brachiopods, largely Prodtictus longispinus, 

 and an upper part which is crinoidal. Neither of these, however, 

 can be compared with the Gallowhill Limestone. As a rule, the 

 Blackbyre Limestoue of this district may be described as essentially 

 a Brachiopod or shelly limestone with occasional bands of Litlio- 

 strotion. The contention of this paper is that the Gallowhill 



