361 
sists of highly inclined shales and sandstone. Mr Charles Maclaren 
was the first to detect organic remains in these strata. About 
twenty -five years ago he found two orthoceratites, but in a frag- 
mentary state. In the year 1857, when the Geological Survey 
extended into the district in question, Mr Geikie first made known 
the richly fossiliferous character of these Silurian strata, the assem- 
blage of fossils unequivocally indicating the horizon of the Ludlow 
rocks of England. On the edges of the upper Silurian beds rest 
unconformably the upper Old Red Sandstones and conglomerates, 
with enormous interbedded sheets of felstone, which form the chain 
of the Pentland Hills. 
The great Lower Carboniferous group is well shown in the area 
embraced by the present map. It occupies the whole of the district 
between the Bathgate hills and the Pentlands, and contains in that 
region a seam of limestone, which is the equivalent of the Burdie- 
house limestone on the east side of the Pentland ridge, and also a 
seam of coal that appears to be quite local. The line of outcrop of 
these two seams, as traced on the map, will show the intricate 
character of the geological details. Perhaps the most remarkable 
feature in the Lower Ccirboniferous series of the Lothians is the 
abundance and variety of its associated contemporaneous igneous 
rocks. There is no well marked zone in the series which does not 
at some locality in this region display its sheets of greenstone, 
felstone, or ash. 
The Carboniferous limestone of this sheet shows characteristically 
the Scottish type of that sub-formation. Its base consists of lime- 
stone bands, with associated shales, sandstone, and coals. Above 
these comes the group of coal-bearing strata, known as the “ Edge 
coals” of Midlothian. But these are not the Coal-measures of 
England, seeing that above them there are bands of limestone, with 
true Carboniferous limestone fossils. The Millstone grit has not yet 
been satisfactorily determined, but its place may be represented by 
some of the thick sandstones of Roslin. 
The Coal-measures proper, or “ Flat coals” of Midlothian, oc- 
cupy the centre of the Edinburgh coal-basin. They are truly the 
equivalents in position as well as fossils of the Coal-measures of 
England. 
It is deserving of remark, that while, in the Lower Carboniferous 
strata and in the “ Edge-coals” of Linlithgowshire, volcanic rocks 
