181 
1916-17.] The Hurlet Sequence and the Abden Fauna. 
and fish remains. Stratigraphically and paleontologically, it is clearly 
the equivalent of the Baldernock Limestone of the type locality near 
Campsie. 
The next limestone horizon in ascending order is perhaps the most 
important in the whole group, namely, the Hurlet Limestone. It cannot 
now be seen in the neighbourhood of Hurlet, the best exposure in the 
district being that seen in the railway cutting at Arkleston. At this 
locality the limestone has a maximum thickness of 31 feet, and is under- 
lain by about 6 inches of alum shale much altered by contact with an in- 
trusive sill. Below the sill comes some 18 feet of shale and fireclay, which 
rests upon the Baldernock Limestone. Unfortunately the Alum Shale 
fauna has not yet been identified in the Hurlet district owing to the 
paucity of exposures. In the Arkleston Section the shale is exceedingly 
thin and much altered by contact with the sill, and though I have searched 
it, I have not yet been successful in finding any fossils. 
The next limestone in ascending order is that known as the Blackhall 
o 
Limestone. It can be examined at Jenny’s Well, near Blackhall, Paisley, 
where it is seen to be in several beds. The upper part, which is about 
24 inches thick, is crinoidal, and contains marine shells ; while the lower 
part, which consists of alternations of bituminous shale and limestone 
over 4 feet in thickness, is entirely composed of ostracods and fish 
remains, the ordinary marine fossils being absent. These characteristic 
features of the Blackhall Limestone have been found to hold good over a 
large area in the Glasgow district. 
Immediately on the top of the Blackhall Limestone there occurs a bed 
of shale, which in the Glasgow district and at Thorntonhall, East Kilbride, 
is exceedingly fossiliferous, and has yielded a somewhat striking faunal 
assemblage. It was first described from the South Hill of Campsie by the 
late Dr John Young, where it lies immediately above the Blackhall Lime- 
stone, and it is fairly well exposed near the top of Baldow Glen, where 
all the characteristic fossils may be gathered. It has been found occupying 
a similar stratigraphical position over a Urge part of Renfrewshire and 
North Ayrshire, and it has been identified to the north of Glasgow, from 
Campsie to Kilsyth, and over a large part of North Lanarkshire, including 
the East Kilbride, Lesmahagow, and Carluke districts. We shall also show 
that it can be traced on the same stratigraphical horizon in the East 
of Scotland. 
The next limestone horizon in ascending order is that known as the 
Main Hosie Limestone. The strata which lie between the Blackhall Lime- 
stone and the Main Hosie Limestone consist for the most part of shales in 
