ORIGIN OF DEPOSITS. DIU7/ 
positions and unbroken condition of the fossils, indicate that the depo- 
sits were marine, and originated in moderately shallow waters, the depth 
probably not exceeding one or two hundred fathoms ; and also that the 
shells inhabited the spots where they now occur. The nature of the 
material constituting the rock is such as would have made, before 
consolidation, a muddy bottom, well fitted for the growth of mollusca ; 
and here we may believe the animals were living and found their 
nutriment before they were entombed. Can we discover the circum- 
stances attending the process of destruction and burial? We have de- 
scribed the overlying bed of basalt, and showed that it flowed in a 
broad submarine stream over the existing bottom of the ocean. ‘That 
there should have been consequently a destruction of life is not re- 
markable ; and we find the effects apparent in the fossils and the con- 
taining rock. The bivalves have the valves almost uniformly united. 
This alone proves that their death was no usual decay, for in such a 
case the valves commonly become scattered. ‘They are sometimes 
gaping a little, though seldom widely, being usually open just about 
as far as the large muscle permits the shell to gape by its relaxation, 
an effect which would naturally proceed from the action of heat under 
water. Some specimens are broken in, as by pressure. Individuals 
.of certain species, especially of Productus and Spirifer, are collected 
together in great numbers, apparently associated in their own natural 
bed of mud. 
The shells, moreover, are mostly silicified, and often present the 
structure of agate or chalcedony; and this effect may be a conse- 
quence of the eruption, for the heated waters take up silica in solu- 
tion, and distribute it widely around. specially would the wet 
mud over which the fused basalt flowed, be well calculated for silici- 
fying the contained shells. ‘The diffusion of this silica is well attested 
by the siliceous concretions, which lie like cannon-balls in the rock, and 
nearly constitute some layers. We cannot resist the conclusion, there- 
fore, that heat occasioned a destruction of life; and the facts already 
detailed have made manifest the effects of heat also in the discoloration 
and hardening of the rocks in which the remains of life were buried. 
Other results of the outburst of basalt are apparent in the scoria and 
basaltic fragments occurring in the overlying sandstone. 
The source of this outflow of igneous rock is an interesting subject 
of inquiry, and the evidence with reference to it is not ambiguous. 
The trend of the air-cells (or mineral nodules filling the cells) has 
often been pointed to as indicating the line in which a stream of 
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