175 
1916-17.] The Hurlet Sequence and the Abden Fauna. 
tory Memoir for this sheet was never issued. An examination of the map, 
however, shows that the Hurlet Limestone position was correctly identified 
over the whole area included in the map from Howood in the south-west 
to Campsie in the north-east. When this district was being mapped the 
Hurlet Limestone and underlying coal were being worked all over the area, 
notably at Hurlet and Campsie, for the Alum Shale, and the characteristic 
features of the limestone and underlying sediments were such that their 
identity over the whole area included in the map could not possibly 
escape notice. 
It may here be pointed out that the officers of the Survey have placed 
on this map the outcrops of the limestones lying below the Hurlet or Main 
Limestone, but at that time these do not appear to have been very accurately 
differentiated. One of the main points which this paper seeks to show is 
that almost immediately beneath the Hurlet Limestone, though generally 
separated from it by a variable thickness of strata, there occurs a limestone 
known as the Blackbyre Limestone, which, because of certain faunal and 
lithological characters, affords a much surer datum line than the Hurlet 
Limestone for correlation purposes, as it can be traced over wide areas 
where the Hurlet Limestone is not conspicuous. It appears to have been 
often confounded with the Hurlet Limestone. 
The Survey Memoir in explanation of Sheet 32 appeared in 1861,* and 
describes the Lower Limestone Series as developed in the neighbourhood of 
Edinburgh, including the districts to the north and south of Bathgate and 
to the south-west of Edinburgh. In the former district Sir A. Geikie 
adopted the West Kirkton Limestone as the boundary line between the 
Carboniferous Limestone and the Calciferous Sandstone Series, and main- 
tained that the Petershill Limestone is the continuation of the 8-foot 
limestone exposed in the Almond Section about 300 feet above the latter. 
In later publications he abandoned f this view, and correlated the Petershill 
Limestone with the Hurlet Limestone. In the course of this paper we hope 
to be able to show that the original correlation was the correct one. 
The explanation to Sheet 33 appeared in 1886, J and includes the two 
important areas of the Lower Limestone Series exposed on the Haddington 
coast at Aberlady and Dunbar. In these two areas the boundary line 
between the Carboniferous Limestone and Calciferous Sandstone Series 
was drawn at the lowest limestone exposed in the coast sections, which has 
* Memoirs of the Geological Survey, Scotland: Explanation of Sheet 32, Edinburghshire 
and Linlithgowshire. 
f Memoirs of the Geological Survey , Scotland: Explanation of Sheet 31 (1879), p. 20. 
% Ibid., Explanation of Sheet 33, Haddingtonshire. 
