SILURIAN EOCKS OF BOHEMIA. 667 



very high angles, and where there are probably convokitions and con- 

 tortions of the beds, there may be such overturns as would cause the 

 appearance of strata containing newer fossils to lie under and amid 

 those containing older ones." But had my late friend visited the neigh- 

 borhood of Prague, he would have learnt that the strata there are not in 

 a state of Alpine confusion, and he would readily have convinced himself 

 that so able an observer as M. Barrande had not been in any way deceived. 

 In fact, the order of superposition is not obscure ; and besides, there is 

 one spot in the suburbs of Piague which I examined, where the inter- 

 calated colonial formation E 1 is reduced in thickness to 6 inches, and 

 where nevertheless it is quite distinguishable by its organic contents, 

 although, as we might have anticipated, there occurs here a slight 

 blending of the distinct faunas, two species of d 4 being associated with 

 a great number of the characteristic fossils of E 1. 



How, then, are we to explain the phenomena ? The facts themselves 

 seem to have been very generally miisunderstood, partly, perhaps, in con- 

 sequence of the use of the term " colony ;" partly for want of distinct 

 names for the two periods, or subdivisions of time, E 1 and E 2. The 

 facts, indeed, themselves are by no means simple, since they relate, first, 

 to the alternate colonization of a certain area by two distinct nations of 

 species ; secondly, to a continual change of character undergone by 

 each of the contemporaneous nations, in consequence of the dying out 

 of old species and the births or first appearances of new ones. M. Bar- 

 rande has been treated very much as an antiquary would be should he 

 pretend to have found monumental evidence of an Anglo-Saxon colony 

 established on Roman ground in the days of the Emperor Justinian ; 

 whereas, there is really no such anachronism in the paleontological 

 facts, as exhibited in Bohemia, and as described by the author of the 

 " Colonial" theory. He simply tells us, in regard to the colony E 1, 

 that out of 63 species, 5 are peculiar to it Avhere it is in its full 

 strength, — in other words, there is a difference between the species of 

 E 1 and of E 2, amounting to about 8 or 9 per cent., indicating a change of 

 no less than one-twelfth of the whole fauna in the interval between E 1 

 and E 2, to say nothing of such discordance as would certainly be found 

 to exist when the rarity of particular species of the first period came to 

 be contrasted with their abundance in E 2, and vice versa. 



Before a geologist is entitled to regard this case as abnormal, or not 

 in harmony with the laws known to have governed the fluctuations of 

 the organic world in bygone ages, he must show that the fauna called 

 D underwent much greater alterations than did the fauna of the mother- 

 country of E 1 and E 2 in the interval of time between the deposit E 1 

 and that called E 2, — in other words, he ought to show that more than 

 a twelfth of the species of D died out, and more than 8 or 9 in 100 of 

 new species came in, in the interval separating d 4 and d 5. Now, so 

 far as I have learnt from M. Barrande, no details have as yet been ascer- 

 tained respecting the fossils of these two subdivisions sufficiently minute 

 to entitle any one to infer that the rate of fluctuation of the two feunas, 



