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Before the end of the Silurian Epoch, according to that accurate census-taker, M. Barrande, they had blossomed forth into no less than 1,622 distinct species.
Professor Ramsay estimates the thickness of the Bala Beds, including the contemporaneous volcanic rocks, stratified and unstratified, as being from 10,000 to 12,000 feet. The Lower Silurian strata were originally divided by Sir R. Murchison into the upper group already described, under the name of Caradoc Sandstone, and a lower one, called, from a town in Carmarthenshire, the Llandeilo flags.
In the Ohio hill, the granite did not break through, though the force of the upheaval was such as to rend asunder the Devonian deposits, for we find them lying torn and broken about the base of the hill; while the Silurian beds, which should underlie them in their natural position, form its centre and summit. This accounts for the great profusion of Silurian organic remains in that neighborhood.
The 'Globigerina' of the Atlantic soundings is identical with that which occurs in the chalk; and the casts of lower silurian 'Foraminifera', which Ehrenberg has recently described, seem to indicate the existence at that remote period of forms singularly like those which now exist.
Scudder, introduces us to the sounds of the Devonian woods, bringing before our imagination the trill and hum of insect life that enlivened the solitudes of these strange old forests. Classification of the Silurian Rocks. Ludlow Formation and Fossils. Bone-bed of the Upper Ludlow. Lower Ludlow Shales with Pentamerus. Oldest known Remains of fossil Fish.
Such appears to be the fact, and I shall therefore conclude with the Arenig beds my enumeration of the Silurian formations in Great Britain, and proceed to say something of their foreign equivalents, before treating of rocks older than the Silurian.
In the last edition of Sir Charles Lyell's "Elementary Geology" it is stated, on the authority of a former President of this Society, the late Daniel Sharpe, that between 30 and 40 per cent. of the species of Silurian Mollusca are common to both sides of the Atlantic.
As a matter of fact they were scarcely more followers of the reformer Calvin than they were of Ignatius Loyola; it was just a symptomatic outbreak of some prehistoric Iberian, Silurian form of worship, something deeply planted in the soil of Wales, something far older than Druidism, something contemporary with the beliefs of Neolithic days.
And finally, beyond all exact human calculation, but estimated at some five million, we reach the Age of Invertebrates in the Silurian, and in the lowest of these rocks we find beautifully preserved fossils of Bryozoans, to all appearances as perfect in detail of structure as these which we have before us to-day in this twentieth century of man's brief reckoning.
The formation is upper Silurian or lower Devonian, a transition to gneiss, but not highly metamorphic. No fossils have yet been found: if any exist they would be microscopic. Where talcose it is bluish, and shows streaks of 'black sand, titaniferous iron. The grey sand washes to white. There are pot-holes which have been filled with either a pudding or a breccia of quartz.
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