TRANSITION AND SECONDARY STRATA. 99 
barrier at their lower extremity. A great number of lakes, is there- 
fore an indication that the region in which they lie, has but recently 
emerged from theocean, and it is remarkablethat the country around 
the Baltic, which is supposed to be rising gradually at this time, 
abounds in them, especially that part of Russia which borders on 
the Gulf of Bothnia, and bears the name of Finland. The south- 
ern States being without lakes, it may be inferred that the era of 
their emergence is exceedingly remote, at least when compared 
with that of Maine, and the other New England States, the ter- 
tiary deposits of the seaboard, of course excepted. 
53. Prop. VII. Since the consolidation of the crystalline or 
•primitive rocks, the earth has undergone a great number of 
catastrophes and revolutions , by which its face has been chang- 
ed. It is probable that in most cases, if not in all, the causes 
of these mutations in its condition and aspect, ivere local, and 
their effects confined to an area of no very great extent. 
The transition and secondary strata are made up chiefly of the 
rounded fragments and ruins of more ancient formations, (Sections 
19 and 21.) The conglomerates, sandstones, clay-slates, lime- 
stones, and beds of clay and sand of which they are constituted, 
do not in themselves possess any high degree of interest. It is to 
the organic remains they hold imbedded that the attention of ge- 
ologists has been principally directed, especially during the last 
30 or 40 years, with a view of ascertaining the different varieties 
of animal and vegetable form and structure that have existed 
upon the earth, and the order of their succession, and thus arri- 
ving at some sound and accurate conclusions respecting the con- 
dition of the globe itself through a long series of ages, and the 
changes to which it has been subjected. The history of the se- 
condary and tertiary strata is therefore, to a great extent, the 
history of organic life during the periods of their formation. 
If the earth was originally a melted mass, it is evident that 
there must have been a time subsequent to the consolidation of 
the primitive rocks, when its temperature was such that water 
could not exist in a liquid state upon its surface, but the existing 
oceans hung as an atmosphere of vapor around the hot and dry 
skeleton of the globe. To this period must have succeeded 
another, when the great mass of the vapor had been conden- 
sed into water — but water not many degrees below the boiling 
point, and in which few animals and vegetables, if any, could 
live. In this condition of things, the vapory and gaseous mass 
surrounding the earth, would bear a considerable resemblance to 
the now existing atmosphere. It would be composed principal- 
ly, as at present, of the incondensible gases, oxygen and nitro- 
gen, but would be highly charged with watery vapour, and pro- 
bably also with carbonic acid. All the phenomena of meteorology, 
eyaporation, condensation, the wearing away of the solid rocks 
by torrents as the rain that fell rushed down to the ocean, and 
the formation of that mixture of fine particles of silica and alumina 
