THE GEOLOGICAL HISTORY OF THE HORSE. 71 
mate then prevailed, and the structure of this great formation shews 
it to be marine. 
Above the old red sandstone is the mountain limestone, in which 
the abundance of what was animated life strikes us with astonish- 
ment. We discern, for the first time, the nautilus, with much 
larger orthroceratites than before, accompanied with spirifera, pro- 
ducta, bellerophon, crinoidea, with an immense number of corals, 
of innumerable varieties of species, and of the greatest beauty, — 
the clear indications of a very hot climate, and also the prevalence 
of the oceanic waters. 
Next in the ascending order is the millstone grit, the greater 
part of which is destitute of organic remains. Now, although 
this formation appears to be oceanic, yet there are many stems of 
vegetables found in it, which most probably, by some of the vio- 
lent perturbations of the surface by volcanic or igneous action, have 
been forced into it, seeing that these stems of plants are all filled 
up with sea sand. A limestone bed succeeds, in which we trace 
scales, jaws, and teeth of many species of reptile fish, with marine 
or fucoid plants, which is considered by the author as a convincing 
proof of the gradual increasing heat of the climate during this 
period, and as preparing for the next most important epoch, — 
namely, that of the great coal formation. Here it is evident that 
the oceanic waters had receded from the northern hemisphere, and 
the surface was covered with magnificent plants, with palms, 
palmacites, shrubs, and arborescent ferns, with reeds in places, of 
thirty or forty feet in height! — and it appears the atmosphere was 
replete with moisture as well as the surface of the earth. Baron 
Humboldt considers that at this period our climate resembled the 
hottest part of South America, whence some of the tributaries of 
the great river of the Amazons flows, which he graphically describes 
thus: — Fresh water streams running in every direction; vegeta- 
tion in places absolutely impenetrable; the moist humid atmosphere 
producing rapid decomposition of the vegetation, and, on the other 
hand, forcing it like a hot-bed, so that some shrubs grow more than 
twenty feet high in one year : hence we naturally account for the 
vast quantity of bituminous coal, which is clearly proved to be 
of vegetable origin. 
After this period the saline waters appear to preponderate, since 
the stems of the plants, &c. are all filled up with sea sand; and the 
proofs appear complete, that the temperature was gradually grow- 
ing colder, since, in the next beds, the fossils are less numerous, 
but they clearly indicate their marine origin. 
In the ascending order he now arrives at the new red sand- 
stone, and this he finds almost a repetition of the old red so much 
below it. In its sandy and frequently finely lamellated structure 
there is abundant proof of oceanic action, and deposition. There 
