Page:The Geologist, volume 5.djvu/32

18 deposits of the same system in various parts of the typical Silurian country, in eight counties of Ireland, in Russia, and in three North American localities. During the Devonian era it existed in several parts of Devonshire, in France, and Germany. Apparently confined to Britain during the earliest stage of its existence, it became more adapted to the world, or the world to it, during the Upper Silurian age, when it reached the maximum of its migratory powers (by no means an ordinary one), and visited many distant parts then; declining in vigour, or satiated with travel, it retired within the European borders during the Devonian period, and there received its dismissal from the stage of life. Emmonsia hemisphærica seems not to have begun life quite so early as its friend which we have just dismissed; its origin dates in Upper Silurian times, when it seems to have been confined to the area of modern America, ranging from the State of Ohio to Tennessee; having outlived the Silurian period, it sent colonies to Spain and Britain, and greatly extended its range in America. Chonophyllum perfoliatum differs from the two former in having always lived within narrow geographical limits; it occurs in Upper Silurian rocks at Wenlock, and in Devonian beds at Ramsley, near Newton Abbott; but its appearance elsewhere is not recorded.

The wide geographical range of the two first of these corals would seem to imply hardy plastic constitutions, fitting them for distant travel and existence under varied circumstances; there is therefore nothing surprising in their extended vertical range; the second, however, seems to have disappeared when at the very zenith of its widely extended power.

The very limited distribution in space of the last of the trio would scarcely suggest the thought that such an organism would be likely to be capable of enduring thermal and other physical changes such as, there are reasons for believing, considerable lapses of time introduce into any given area, changes probably not dissimilar to those experienced in passing to a distant locality in any one and the same period. On the other hand, the well-known fossil coral Favosites Goldfussi occurs in Devonian rocks in Devonshire, at Nehou and Visé in France, at Millar in Spain, in the Oural in Russia, in the States of Ohio and Kentucky in North America, and in New South Wales; it was the most decided cosmopolite of the Fauna to which it belonged, the greatest traveller of its day, the earliest Devonian that circumnavigated the globe, the prototype of the Drake of a later age. It seems to have successfully struggled with the varying conditions consequent upon change of place, and might have been expected to be just as capable of contending with such as depend on lapses of time; nevertheless, the facts do not harmonize with such conclusions. Chonophyllum perfoliatum formed part of the Silurian and Devonian Faunas, but was confined to the British area; Favosites Goldfussi was at home in every part of the world, yet it commenced and terminated its career within the Devonian period.

The rocks of Devon and Cornwall have fifty eight species of fossils