FACTS AND OBSERVATIONS. 



species of Orthoceratite in New York, one eighth outlive their native deposit, while in Britain twice 

 that number do (twelve species out of fifty-one) . In Britain all the Pleurotomaria are constants ; 

 but in other areas many make short runs upwards. 



The species and genera probably differ, in their tendency to recur, according to the stage in 

 which they make their first appearance ; and it is believed that considerable diversities of behaviour 

 are discernible in them. Time has not permitted the recurrency of the higher portions of the 

 Silurian system to be looked at with sufficient care ; but we see it to be large, and to become doubly 

 interesting from the near approach of the Devonian system, and of the extra-epochal or serial 

 recurrents it initiates. 



The question may arise whether a fossil apparently recurrent be not in truth a new and 

 independent creation not a recurrent, but the identical species of a past horizon, brought into 

 existence a second time. The possibility of such an occurrence is denied by most of the authors of 

 the present day. But on such a subject it is better not to be too confident. Creation is a mystery 

 which all our efforts to penetrate, as Elie de Beaumont says, have only raised a very small corner of 

 the thick veil under which nature has concealed her immense work. It is the opinion of Agassiz 

 that animals undistinguishable from each other may appear, without tie or connexion of any sort, in 

 different fauna (Proc. Acad. Nat. Science, Philad. 1859, p. 186). Dana (Ann. Nat. Hist. 2nd ser. 

 vol. xvii. p. 43) affirms and advocates the doctrine of independent creations. Bronn, from reasons 

 altogether different from Dana, broadly states that " there is no doubt but that the return of iden- 

 tical life-conditions can cause groups of animal species to appear a second time " *. Analogous 

 observations relating to the Oolite near Cheltenham f, and to the Cornbrash near Cirencester J, are 

 in accord with this. The mixed beds of Petite Coeur in the Tarentaise, and consisting of Carbo- 

 niferous, Liassic, and Jurassic rocks, as investigated by Elie de Beaumont , Mortillet ||, Heer ^[, and 

 others, greatly favour the opinions of the Heidelberg and Newhaven Professors. 



I beg to express a waiting belief in this hypothesis, without being quite able to conceive the 

 possibility of any organism resisting the plutonic and other agencies so terrible and so active during 

 the long interval with which we are dealing. But Edward Forbes, Pictet, Deshayes, and a 

 numerous company of good naturalists, who do not believe in a second creation, doubtless have 

 offered strong reasons in support of their incredulity. 



DIVERGENCE. A few words on this subject may be useful. By this expression is meant a change 

 of residence made by any member of a molluscan fauna from ground to ground, once or more than 

 once. With sediment, in fact, its connexion is often indirect and at second hand. 



Divergence is rendered possible by a pliable organization, and it is necessary in order to enable 

 mollusks to travel (migrate) , to pass over and feed on a plurality of grounds, and also to tolerate 

 changes in the nature of their habitats. 



The present state of the ocean -floor, as far as inorganic matter is concerned, I believe, reflects 

 very tolerably that of any part of the earth's history. The materials and the agencies have always 

 been much the same ; but with living beings it is different. 



Although a sediment may be, and often is, the same in two or more epochs to every test of the 

 chemical analyst, each of these epochs, as was taught by Mr. S. P. Woodward, had its own 

 appointed and very different forms of life. 



Composed of few mineral substances, sediments still vary in the proportions of their ingredients 

 so much and so frequently as often to break up the bottoms into small and irregular areas. Of 

 course any quantitative mineral analysis has only a very limited application as to place. 



* Bronn, Essai pour la Prix, 1856, Acad. des Sciences ; Comptes Eendus, torn. ii. p. 724. 



t Lycett, Morris, Ann. Nat. Hist. 1848, vol. ii. p. 248 &c. Paljeontogr. Soc. 1850-3. Brodie, Geol. Journ. 

 Lond. vol. vi. p. 239. 



J Buckman, Ann. Nat. Hist. vol. xii. p. 324 (1853). Bullet. Soc. Geol. de France, vol. xii. pp. 534, 676. 



|| Bullet. Soc. Ge'ol. de France, vol. x. p. 18. ^ Jahrbuch f. Mineral, 1850, pp. 657, 674. 



