Cambrian, and Silurian times, we only deal with sea bottoms. It may reasonably be asked: What like then were the rocks whose detritus formed the sea sludge from which the Laurentian system was built up? And again: What forms of life, animal and vegetable, dwelt on the dry land washed by Laurentian, Huronian, Cambrian, and Silurian seas? The geologist's answer must be, and that in all reverence, "God only knows." These periods, to our limited knowledge, are the borderland dividing Time from Eternity.
Our Devonian beds in Pembrokeshire are not rich in relics. At Freshwater East there is a fossiliferous rock, filled with small shells; and at Skrinkle, near Lydstep, there is a fish bed lying on the junction of the Devonian and Carboniferous. The Devonian fish were chiefly ganoids, im which the inner skeleton is cartilaginous, but the scales make up for this deficiency by their strength: the sturgeon is a modern instance.
In the very interesting Carboniferous period, we are in Little England well supplied with examples. All along our southern coast are grand cliffs of carboniferous limestone, the glory of our land. These were the bottom of the deep sea in Carboniferous times, and are stored with corals and lily-like crinoids, growing from their root, with stem and flower; oysters then as now were natives of Pembrokeshire; the little snail-like Bellerophon lived in this sea, at Haroldstone, near Haverfordwest; as did the bivalve Producta, at Manorbier; both, perhaps, providing food for the shark-like Cochlioldus, which has left its shell-crushing teeth in the limestone of Giltar. On reaching Tenby the limestone ocean shallowed, and we get to millstone grit. This was deposited in shoal water. We find in this, those stones which, when sawn in two and polished, are called by the Tenby folks beetle-stones. They are really some organic matter (fish coprolites, perhaps) which, in rolling about on the slimy bottom of the millstone grit waters, collected round themselves a coating of clay; then gases formed in the nueleus, and cracked it, without bursting the enveloping clay; in future ages these cracks were filled up by spar. The pebble on being cut and polished, very fairly simulates a beetle, the body of the insect being represented by the fish dung, the legs by the gas cracks filled with spar. Passing on towards Saundersfoot, we come to the regular coal measures. In this neighbourhood, during the Carboniferous period, there grew in soil, half sand, half slime (much the same as we found under the millstone grit waters), a forest of Calamites, giant horse-tails, or equiseta; these ran up some twenty feet without a branch, the foliage springing directly from the cane, as it does in the common horse-tail. An undergrowth of suckers breaking up from the roots of the Calamites made thick bushes; with these grew another plant of which we now only find the pith sigillaria, and the roots stigmaria. Then as now Saundersfoot was draped with ferns. We find at least three sorts: pecopteris, neuropteris, splenopteris. All these plants grew either in, or on, the banks of, a lagoon, and the country was gradually sinking. When it sank below the sea level then water rushed in, and with it mud. After awhile fresh vegetation grew, and the process was repeated. It can scarcely have been a healthy neighbourhood for man; but that did not much matter, since the ruling inhabitants of the earth in those days were huge frogs called Labyrinthodonts, and even these were non-resident at Saundersfoot.
This period of feathery canes and ferns was a time of great unrest in Pembrokeshire. The earth’s crust being constantly on the move, now rising, now falling, the result was that the coal formed did not retain its gases, and is of the kind known as anthracite. In our days earthquakes are fortunately but feeble phenomena in the British Isles; yet when they do occur, Pembrokeshire still trembles as from the recollection of past terrors, for a volcanic vein runs under us.
When the Carboniferous age terminated, a veil falls over the history of the land. The Permian age came and went; the great secondary series of formations was followed by
