134 PROCEEDINGS OF THE 



factory, and must always be so wherever we have to deal with 

 mixed sedimentary materials, for we have every amount of purity 

 between what we consider a cannel coal, and bituminous shale, 

 according to the presence or absence of earthy impurities in the 

 deposit. 



I have dwelt upon this point in order to show how impossible 

 it is to draw a line between these coaly shales and the cannel coals 

 themselves. Many of these shales, which owe their hydro-carbon 

 to the presence of vegetable matter only, are at present being 

 worked for the oil they contain, and afford a lighter and better 

 paraffin oil than that distilled from some of the cannel coals. 



This may be owing to the clay base of the shale retaining more 

 of the original volatile products, which in the other case have 

 escaped from the cannel coals, leaving in them only the heavier 

 products obtained by distillation. 



Besides these coaly shales of vegetable origin, we have another 

 class in our Scottish coal-field which appears to owe its oil to the 

 great amount of animal organisms that have died in the beds. 

 They are in general of a dark grey, or brownish colour, and are 

 known to the miners of the West Calder district as the Fern-spore, 

 or seed-cake beds, from the immense number of minute shells 

 which dot their surface. The organisms which make up the great 

 bulk of these beds are Entomostraca — a family of small bivalve 

 crustaceans — and a few scattered fish and plant remains. The 

 Entomostraca of the West-Calder shales belong principally to one 

 species — the Cypris Scoto-Burdigalensis; or, it has been more correctly 

 determined by Professor Jones to be, the Leperdita OJceni of Count 

 Miinster. 



These little Crustacea seem to have swarmed in vast numbers in 

 the seas of the carboniferous period, as their remains, in some 

 cases, make up certain bauds of these oil shale strata, which, on 

 distillation, yield a paraffin oil of fine quality. 



As far as I am aware, no one has hitherto noticed the animal 

 origin of the soil in these shales. It was while I was engaged in 

 the working-out of the Entomostraca of our other coal-strata, that 

 I was struck by their very great abundance in the beds in question, 

 and have come to the conclusion in my own mind that these shales 

 owe their oil to the amount of these minute Crustacea which have 

 died upon the sea or lake bottom, and not to the decay of plants, 

 as in the vegetable oil shales. 



