of Edinburgh, Session 1883-84. 527 
From the data now advanced it appears possible to deduce other 
conclusions important from a geological point of view. In the de- 
posits due essentially to the action of the ocean, we are at once 
struck by the great variety of sediments which may accumulate in 
regions where the external conditions are almost identical. Again 
marine faunas and floras, at least those of the surface, differ greatly, 
both with respect to species and to relative abundance of individuals, 
in different regions of the ocean ; and as their remains determine 
the character of tbe deposit in many instances, it is legitimate to 
conclude that the occurrence of organisms of a different nature in 
several beds is not an argument against the synchronism of the 
layers which contain them. 
The small extent occupied by littoral formations, especially those 
of an arenaceous nature, shown by our investigations, and the 
relatively slow rate at which such deposits are formed along a 
stable coast, are matters of importance. 
In the present state of things there does not appear to be anything 
to account for the enormous thickness of the clastic sediments 
making up certain geological formations, unless we consider the 
exceptional cases of erosion which are brought into play when a 
coast is undergoing -constant elevation or subsidence. Great move- 
ments of the laud are doubtless necessary for the formation of thick 
beds of transported matter like sandstones and conglomerates. 
In this connection may be noted the fact that in certain regions of 
the deep sea no appreciable formation is now taking place. Hence 
the absence, in the sedimentary series, of a layer representing a 
definite horizon must not always be interpreted as proof either of 
the emergence of the bottom of the sea during the corresponding 
period, or of an ulterior erosion. Arenaceous formations of great 
thickness require seas of no great extent and coasts subject to 
frequent oscillations, which permit the shores to advance and retire. 
Along these, through all periods of the earth’s history, the great 
marine sedimentary phenomena have taken place. 
The continental geological formations, when compared with marine 
deposits of modern seas and oceans, present no analogues to the red 
clays, Radiolarian, Globigerina, Pteropod, and Diatom oozes. On 
the other hand, the terrigenous deposits of our lakes, shallow seas, 
enclosed seas, and the shores of the continents, reveal the equivalents 
