in the Coal-Measures of Nova Scotia. 219 



under the microscope, the same prismatic and tubular ar- 

 rangements which characterize the shells of living mollusca. 

 Sections also of the same shewed what may be part of the 

 columella and spiral whorls, somewhat broken and distorted 

 by pressure and crystallized. The genus cannot be made 

 out, as the mouth is wanting. If referable to a Pupa or any 

 allied genus, it is the first example of a pulmoniferous mol- 

 lusk hitherto detected in a primary or paleozoic rock. 



Sir Charles next proceeded to explain his views as to the 

 origin of coal-fields in general, observing that the force of 

 the evidence in favour of their identity in character with the 

 deposits of modern deltas has increased in proportion as they 

 have been more closely studied. They usually display a vast 

 thickness of stratified mud and fine sand without pebbles, 

 and in them are seen countless stems, leaves, and roots of 

 terrestrial plants, free for the most part from all intermix- 

 ture of marine remains, circumstances which imply the per- 

 sistency in the same region of a vast body of fresh water. 

 This water was also charged like that of a great river with 

 an inexhaustible supply of sediment, which had usually been 

 transported over alluvial plains to a considerable distance 

 from the higher grounds, so that all coarser particles and 

 gravel were left behind. On the whole, the phenomena imply 

 the drainage and denudation of a continent or large island, 

 having within it one or more ranges of mountains. The 

 partial intercalation of brackish water beds at certain points 

 is equally consistent with the theory of a delta, the lower 

 parts of which are always exposed to be overflowed by the 

 sea even where no oscillations of level are experienced. 



The purity of the coal itself, or the absence in it of earthy 

 particles and sand throughout areas of very great extent, is 

 a fact which has naturally appeared very difficult to explain, 

 if we attribute each coal-seam to a vegetation growing in 

 swamps, and not to the drifting of plants. It may be asked 

 how, during river inundations capable of sweeping away the 

 leaves of ferns, and the stems and roots of Sigillariae and 

 other trees, could the waters fail to transport some fine mud 

 into the swamps % One generation after another of tall trees 

 grew with their roots in mud, and after they had fallen pros- 



