00 TRANSITION SERIES. 
Chapter VII. 
Strata of the Transition Series. 
Thus far we have been occupied with rocks, in 
which we trace chiefly the results of chemical 
and mechanical forces ; but, as soon as we enter 
on the examination of strata of the Transition 
Series, the history of organic life becomes asso- 
ciated with that of mineral phenomena.* 
The mineral character of the transition forma- 
tions presents alternations of slate and shale, 
with slaty sandstone, limestone, and conglomerate 
rocks ; the latter bearing evidence of the action 
of water in violent motion ; the former showing, 
by their composition and structure, and by the 
organic remains which they frequently contain, 
that they were for the most part deposited in the 
form of mud and sand, at the bottom of the 
sea. 
Here, therefore, we enter on a new and no 
less curious than important field of enquiry, 
* It is most convenient to include within the Transition series, 
all kinds of stratified rocks, from the earliest slates, in which we 
find the first traces of animal or vegetable remains, to the termi- 
nation of the great coal formation. The animal remains in the 
more ancient portion of this series, viz. the Grauwacke group, 
though nearly allied in genera, usually differ in species from those 
in its more recent portion, viz. the Carboniferous group. 
