Carboniferous Period in East Scotland. 247 
which gave sustenance to innumerable swarms of entomostraca and other 
small animals that supported the smaller acipenseroid fishes which, in turn, 
supplied the food of the larger crossopterygian forms, as attested by the 
indigestible remains found in the coprolites that are of common occurrence 
in the Lothian Oil-Shales. Although the step-like depressions that the 
country was undergoing sometimes allowed the estuarine sea water to invade 
these lagoons and carry into them such marine forms as those associated with 
the Dalmahoy, Pumpherston, Dunnet, and Fraser Shales, it is not necessary 
to conclude that the whole fish fauna was of estuarine character. Lung-fishes 
of the genera Uronemus and Ctenodus have left their remains with the oil- 
shale to attest to their freshwater origin. It is probable, therefore, that it is 
to the surplus of this lowly plant life that was not consumed by the animals 
that we must look for the main source of the hydrocarbons of the oil-shale, 
while the animal remains supplied the larger part of the nitrogenous matter. 
That the higher land vegetation surrounding the lagoons may have supplied 
a small amount of the material is just probable, but, if so, it must have been 
so well macerated by the water that the structures were so completely 
obliterated by decomposition brought about by the micro-organisms, as to 
leave no traces discoverable by the microscope. The beautiful state of 
preservation of such forms as Zelangiwin (Sphenopteris) affine and Lepidophoios 
that are so common features in some of the oil-shales, militates strongly 
against such a supposition. The small—almost infinitesimal—remnant of 
material extractable by the ordinary solvents is greatly against the supposition 
that lycopodiaceous spores may have been swept into the lagoons after the 
manner of pollen during what are popularly known as “sulphur showers.” 
Mr Steuart says in his chapter that some oil-shales are largely made up of 
entomostraca. There is a regular passage of oil-shale into limestones of the 
Burdiehouse type, and every gradation can be found in the field. In the 
clear water parts of the lagoon where the entomostraca were able to dispose 
of the plankton as it arose, the constant accumulation of their exuviee and 
their shells, at death, would easily give rise to limestone of Burdiehouse type. 
VULCANICITY DURING THE DEPOSITION OF THE OIL-SHALES. 
As already stated there were two regions, one on each side of the Oil- 
Shale area, where volcanoes were active throughout the whole period of their 
production, viz. that of the Garleton Hills towards the east and of the Campsie 
Fells to the west. In both regions the volcanic plateau became subaerial 
and subject to atmospheric denudation. It is highly probable that these 
plateaux supplied material to form the peculiar mud-like clays with calcareous 
ribs that are known as the Marls, which occur along with the Houston Coal, 
