178 Proceedings of the Royal Society of Edinburgh. [Sess.. 
recent revision, and we find that it adopts the Hurlet datum line as given 
in the map of 1878, which in Sheet 30 we regard as being everywhere 
correct. A valuable advance, however, is made in this Memoir, as the two 
important limestone horizons lying below the Hurlet Limestone, known 
respectively as the Blackbyre Limestone and Hollybush Limestone, are 
differentiated out and correlated with other exposures in the district. 
The overlying limestones all formerly grouped together as the Hosie 
Limestone are also differentiated out and correlated throughout the area 
under consideration. 
In a series of papers published in the Transactions of the Geological 
Society of Glasgow* the present writer, following up the work of the 
Survey, has been enabled to show that the various members of the Lower 
Limestone Series can be traced over large parts of Ayrshire, Renfrewshire, 
Lanarkshire, and Stirlingshire, not only by lithological characters and 
stratigraphical relationships, but also by the fact that the various fossili- 
ferous horizons are characterised by certain faunal associations or group- 
ings indicative of similar widespread physical conditions of deposition. 
These we believe to obtain over a large part of the West of Scotland, 
and it is the purpose of this present paper to attempt to trace them into 
the East of Scotland. Perhaps the most important of these faunal associ- 
ations is that which occurs on the horizon of the Hurlet Alum Shale 
between the Blackbyre Limestone and the Hurlet Limestone. In one of 
the papers just referred to, the value of this fossil group in the 
establishment of the Hurlet datum line has already been discussed in 
some detail. f 
To Mr A. Macconochie J belongs the merit of first correlating the 
Bilston Burn Section south-east of Edinburgh with that exposed between 
Kinghorn and Kirkcaldy on the other side of the Firth. One of the 
strong points in his correlation is the identification of the faunal associ- 
ation found below one of the lower limestones of the Bilston Burn with 
that occurring below the first Abden Limestone of Fife, a correlation 
* “On tlie Distribution of Posidonomya corrugata , Eth. jun., in the Carboniferous Lime- 
stones of the Glasgow District,” by P. Macnair and H. Conacher, Trans. Geol. Soc. Glasgow , 
vol. xiv, p. 309, 1912 “ The Stratigraphy of the Limestones lying immediately above 
the Calciferous Lavas in the Glasgow District,” by P. M.icnair and H. Conacher, ibid., 
vol. xv, p. 37, 1913. “The Hurlet Sequence in North Ayrshire,” by Peter Macnair, ibid., 
vol. xv, p. 200, 1914. “The Hurlet Sequence in North Lanarkshire,” by Peter Macnair, 
ibid , vol. xv, p. 387, 1916. 
f “The Hurlet Sequence in North Ayrshire,” Trans. Geol. Soc. Glasgow , vol. xvi, p. 200, 
1914. 
+ Memoirs of the Geological Survey of Scotland : The Geology of the Neighbourhood of 
Edinburgh, p. 611. 
