286 PEOCEEDINGS OF THE GEOLOGIGAL SOCIETY. 



great in Britain, &c.). All tliis produces a set of changes which 

 are local and limited, so that the universal scheme is not every- 

 where worked up to the same point at the same instant. Here 

 preparations were being made by vertical oscillations for SUuiian 

 deposits, there for Devonian, the older beds having been already 

 laid down. Suppose for a moment, that the crust of our planet pos- 

 sesses 50 groups of sedimentary strata, 50 epochal horizons in fact ; 

 none of these in their several localities were necessarily formed at the 

 same time ; so that absolute isochronism in groups cannot be com- 

 mon. Sir Henry De la Eeche* hints at this. Barrande f in like 

 manner admits, not an absolute synchronism of faunae, but only 

 relative contemporaneousness in the flux of time — a proximity of 

 existence. All faunae and florae were individually perfect from the 

 very earliest epochs, and many were highly organized %. We see this 

 in the complex eye of the Trilobite found in the Potsdam Sandstone 

 of the Upper Mississipi, in the Hymenocaris of the Welsh Lingula- 

 flags, and in other less striking cases. 



During the palaeozoic and other geological periods, there were two 

 kinds of provinces, circles, or centres of life : — the " geographic," 

 which occupied the same horizon in scattered centres, each having 

 its own population more or less peculiar ; and the " epochal " or 

 " geological," which, with the advance of science, are every day be- 

 coming more numerous in many parts of the world. They exist on 

 their own distinct horizons, and are confined each to a single condi- 

 tion of things, denominated an epoch or a formation. The same 

 epochal province may contain many geographic circles, or possibly 

 only one. Both the geographic and epochal circles will soon become 

 of high importance, as the means of reconstructing or restoring to 

 the mind's eye, though imperfectly, the earth's surface, its configu- 

 ration and contours, at the different epochs. The members of these 

 faunae, aided by sun-cracks, ripple-marks, animal-tracks, and such- 

 like, will be used as guides from land to land, in the same way as 

 Plants were used by the late Edward Forbes, and the Molluscs of 

 the present day by M^Andrew, connecting and disconnecting large 

 and interesting portions of the earth in historic geology. As re- 

 gards the geographic province, I am not sufficiently iustructed in 

 Agassiz's hypothesis of the simultaneous (or nearly simultaneous) 

 planting of many such over the surface of the earth during any 

 given epoch, to give any opinion about it. At present, I am content 

 to say that, the great laws of animal distribution beiug the same 

 then as now, zoological provinces were everywhere formed, but 

 each with a far wider diffusion than at this day ; for, from their 

 great size, from the rarity of coast-lines, change of place was made 

 easy to their inhabitants in search of food and shelter. Near to the 

 means of subsistence they would naturally crowd. Examples of 

 geographic provinces in the palaeozoic series abound, and are very 

 striking. Thus, in Eussia, De VerneuU found 205 species cxclu- 



* Mem. Geol. Surv. vol. i. p. 103. 



t Syst. Sil. Boheme, p. 72 c. 



\ Murchison, De Verneuil, and Keyserling, Russia, vol. ii. p. xxx. 



