284 NOTICES OF THE MEETINGS [March 18, 
Sections also of the same showed 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 mollusk hitherto detected in a primary or palzeozoic 
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 intermixture of 
marine remains, circumstances which imply the persistency 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 sedi- 
ment, which had usually been transported over alluvial plains to a con- 
siderable distance from the higher grounds, so that all coarser par- 
ticles 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 in~ 
tercalation of brackish water-beds at certain points is equally con- 
sistent 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 par- 
ticles 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 Sigil- 
lari 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 prostrate 
and had been turned into coal were covered with layers of mud 
(now turned to shale), and yet the coal itself has remained unsoiled 
throughout these various changes. The Lecturer thinks this enigma 
may be solved, by attending to what is now taking place in deltas. 
The dense growth of reeds and herbage which encompasses the 
margins of forest-covered swamps in the valley and delta of the Mis- 
sissippi, is such that the fluviatile waters in passing through them, are 
filtered and made to clear themselves entirely before they reach the 
areas in which vegetable matter may accumulate for centuries, forming 
coal if the climate be favourable. There is no possibility of the least 
intermixture of ‘earthy matter in such cases. Thus in the large sub- 
merged tract call the ‘* Sunk Country,” near New Madrid, forming 
part of the Western side of the valley of the Mississippi, erect trees 
have been standing ever since the year 1811-12, killed by the great 
