174 Proceedings of the Koyal Society of Edinburgh. [Sess. 
at a much more accurate conception of the stratigraphical and palaeonto- 
logical characteristics of the Lower Limestone Series of the West of Scotland, 
and we are therefore in a much better position to institute a comparison 
with the East of Scotland sections than we were before. One of the most 
remarkable and important of all the fossiliferous horizons in this series is 
that found in the Hurlet Alum Shale just below the Hurlet Limestone. 
This faunal association is characterised by a brachiopod bed, a lamelli- 
branch bed, and a bone bed. The fauna has been discovered on the same 
stratigraphical position over a large area in the West of Scotland, and a 
similar fauna has been found below the Hurlet Limestone at Charlestown 
and Abden in Fife, and on the same horizon in the Bilston Burn and at 
Aberlady Bay and Dunbar in the Lothians. 
II. Classification of the Carboniferous Limestone Series 
of Scotland. 
The Carboniferous Formation in the Midland Valley of Scotland has been 
divided into the following four main subdivisions: — 1, The Coal Measure 
Series; 2, The Millstone Grit Series; 3, The Carboniferous Limestone Series; 
and 4, The Calciferous Sandstone Series. The Carboniferous Limestone 
Series has been further subdivided into the following three groups : — 
^(3) Upper Group of three or more limestones, with thick 
beds of sandstone and coal. 
(2) Middle Group, containing several workable seams of 
coal, with Clayband and Blackband Ironstones 
associated with sandstones and shales, but with no 
limestones. 
(1) Lower Group, comprising several beds of limestone 
with sandstones, shales, some coals, and ironstones. 
Carboniferous 
Limestone Series 
The group of limestones and associated strata to be discussed in this 
paper are practically all included in the lowest of the above three sub- 
divisions, though some of the lower members are classed by the Geological 
Survey with the Calciferous Sandstone Series. We regard this line of 
demarcation as of a purely conventional character, and do not consider 
that it marks any important stratigraphical or palaeontological break in 
the Carboniferous System. 
III. Historical Review. 
The Geological Survey began work in Scotland in 1854, and the map of 
the Hurlet district was published in 1878, but, unfortunately, the Explana- 
