My uncle first shewed us some bits of hornblende, primary limestone, mica-slate, and granite, as specimens of the inferior order, or ancient primitive rocks, destitute of all organic remains, and having something of a crystalline appearance.
Next he shewed us the drawers containing the transition or submedial series, including grey wackè, transition limestone, quartz, common slate, and serpentine; they contain some specimens of the lowest scale of organized beings, such as zoophytes, madrepores, and testacea, but very sparingly, and all different from those now known.
Then came the medial order, or carboniferous rocks of old red sandstone, mountain limestone, and all the parallel strata of coal, slate-clay, and freestone, which he calls coal measures. He shewed us abundant remains in them of animals, but very few of which have any resemblance to existing species. Some of the limestone or marble specimens were polished on one side, so as to shew their beautiful veins and colours. On several bits of the coal and black slate, I saw the impression of leaves, branches, and seeds, but no shells, or any kind of animal remains: there was one perfect fern leaf, but my uncle says, of an unknown family, and a great many reeds. There was also, a flat block of greyish freestone, on which the regular scales of some seed vessel, like a very large fir cone, were deeply marked; and on another, I am sure I could distinctly trace the imbricated form and the spines of the common prickly pear of the Brazils. Indeed, my uncle thinks that all these vegetable remains seem nearly allied to the plants of tropical climates; and he says, it would be a most interesting employment for some naturalist to devote himself to the study of what might be called subterranean botany. These coal measures occupy several drawers; for besides the Staffordshire, Newcastle, and other coals, he has specimens of the seventeen coal beds of the forest of Dean, and a large collection of their organic remains, which he has taken great pains in arranging.
The next drawers contain the supermedial series, beginning with the magnesian limestone, new red sandstone, and red marl. There are very large districts of this formation in the central parts of England, and they include the great deposits of rock-salt, which is of so much importance, he says, to the empire. Considerable beds of gypsum are also found; but it contains no organic remains of either animals or vegetables. Above these,—for you no doubt have perceived what I forgot to mention, that my uncle began at his lowest drawer, in order to shew the lowest strata first,—above these, he showed me a collection of the lias and oolite strata, both of them impure limestones, but extremely rich in the number and variety of organic remains. These consist of ferns and flags, corals and zoophytes, shells of all kinds, univalve, bivalve, and multivalve; ammonites of all sizes, fishes of several species, and turtles and other amphibia unlike any of the species now known. To one of these amphibia has been given the name ichthyosaurus, which, my uncle says, means the fish-like lizard; it having the head of a crocodile and the back bone of a shark; he has only a small specimen, which stands over the book-case, but he says some have been found in the lias near Lyme, in Dorsetshire, three or four feet in length. And he told me that at Stonesfield, near Woodstock, in Oxfordshire, the fossil remains of another extraordinary animal of the amphibious tribes was discovered, which has been called the monitor; no complete skeleton of it has yet been put together, but many of the detached parts must have belonged to an animal forty feet long, and twelve feet high!
The remainder of this numerous series consists of different strata of sands and clays, and various limestones, up to the chalk formation; and they contain a repetition of the fossils he shewed me in the lower parts of it. He frequently made me observe, that these fossils are all not only very widely distinguished from the families found in the carboniferous and transition series, but that there are also striking peculiarities in themselves according to the bed which they occupy.
We came next to the great chalk formation, with its wonderful deposition of flints in parallel layers; and then to the last, or superior order, consisting of gravel or sand, or of clay, which is in some places four or five hundred feet thick, and resting on the chalk. Its organic remains are highly interesting; but my uncle said he would not perplex our memories at present, by a minute examination of the specimens in his collection; he wished to give us general ideas, hereafter we may study the particulars. Before he closed his drawers, he shewed us, that below this upper formation all the remains of organic bodies were in a petrified or mineralized state; that is, the general structure and external form of the body has been preserved, but the original matter of which it was composed has entirely disappeared, and has been replaced by the substance of the mineral in which it was imbedded. On the contrary, in the strata which cover the chalk, the shells are merely preserved, and in such a state, that when the clay or sand in which they lie is washed off, they might appear quite recent, if they had not lost their colour and become more brittle. My uncle shewed us a few specimens of these, and also of some shells, which he says are peculiar to fresh water, but which are often found in alternate layers with the marine shells, as if they had been deposited by alternate inundations of fresh and salt water. And lastly, he shewed us some of the shells found in a horizontal stratum of gravel on the coasts of Essex and Suffolk, about fifty feet above the sea, which are exactly the same with the shells at present existing in the sea on the same coast. Above all these regular strata, he says, there is in many places spread a confused covering of gravel, apparently formed by the action of a deluge, which had shattered and rounded the fragments of the rocks over which its torrents had swept.
In this gravel the remains of numerous land quadrupeds are found; many of them of species now unknown, such as the mastodon, and mammoth or fossil elephant, with varieties of the hyæna, bear, rhinoceros, and elk, but indiscriminately mingled with others, which still exist in the country.
I have taken a good deal of pains to acquire a clear idea of this order of the strata, with their vegetable and animal remains. My uncle did not shew them all at one time, we went over them by degrees, a little every day; but I have just summed them up altogether, to give you an idea of what I have seen.
24th, Good Friday.—Before we went to church to-day, my uncle spoke to us for a short time on the solemn event we were going to commemorate; and though my notes of what he said can be of little use to you, yet I am anxious to shew my dear mamma that I take still more pains to profit by what he tells us on this most important subject, than upon Geology or any thing else.
“You are all too well acquainted with Scripture,” said he, “not to know that the lesson which it everywhere inculcates, is, that man by sin and disobedience had fallen under the displeasure of his Maker, and that there was an invincible necessity, however inexplicable to our comprehension, that our Saviour should lay down his life to redeem us from that sin, and to procure for repentant sinners forgiveness and acceptance.