306 
The plains of Mariqnita are more or less covered with thick 
beds of gravel, in which are found fossil trunks of coniferae, 
fern-trees, corals, and the remains of crocodiles, similar to 
those now flourishing in that zone. The old sedimentary beds 
resting on the primary base contain deep-sea shells and corals, 
similar to those seen along the beach on the Chilian coast. As 
we ascend the series, we find there seams of coal, containing in 
the inter-stratified black shale impressions of fern-leaves, but 
not very abundant. Above these are argillaceous beds in- 
closing a variety of shells and the remains of fishes. On 
these, again, are deposited several calcareous beds containing 
fossils in abundance, such as ammonites, hamites, &c., 
some of which were described and figured in the Journal 
of the Geological Society by the late Professor Forbes in 1844. 
These fossils were collected in situ, and presented to the 
Geological Society by me in 1843. Amongst them were eight 
new species. Finally, the upper part of this great sedimentary 
formation forms the plains of Bogota, where we find again 
deposits of sand and gravel containing the relics of gigantic 
ammonites and oyster-shells. I examined the eastern flank of 
this branch of the Andes to the sources of the rivers Orinoco 
and the Amazon, and found very extensive beds of similar 
character to those seen on the other side ; but all their organic 
contents, with the exception of the ammonites and hamites, 
were of the same description as those now existing on the 
coast of South America. I have obtained from white clay 
seams, impressions of leaves with their green and yellow 
colours partially preserved, which indicates . that the 
formation could not have been of great antiquity. As we 
proceed northward, we find the sedimentary beds much more 
developed than they are in thfe south, and containing tropical 
remains, even in high latitudes. If we take Nova Scotia, for 
example, we find the lower beds enclose only a few deep-sea 
shells, somewhat similar to those still living in the south. 
These are covered by the carboniferous beds, in which are 
entombed tropical vegetation, such as fern-trees, catamites, 
&c., with reptiles of the existing tropical character; and on 
these coal-seams, again, are various beds of sandstone-clay 
and gravels. 
I need not dwell further on this subject, as I trust I have 
sufficiently shown that, although the order of the sedimentary 
beds is never found inverted, their development in different 
countries is not the same; and the periods of their deposition 
have been very variable, and that, therefore, they cannot be 
correlated as to their ages. 
