276 * COSMOS. 



and then uninterruptedly on through all formations to the 

 strata of the tertiary period, while Saurians begin with the 

 zechstone. In like manner, we find the first mammalia 

 ( Thylacotheriimi Prevostii, and T. Bucklandii, which are 

 nearly allied, according to Valenciennes,* with marsupial an- 

 imals) in the oolitic formations (Stonesfield schist), and the 

 first birds in the most ancient 6retaceous strata. t Such are, 

 according to the present state of our knowledge, the lowest$ 

 limits of fishes, Saurians, mammalia, and birds. 



Although corals and Serpulidas occur in the most ancient 

 formations simultaneously with highly-developed Cephalopodes 

 and Crustaceans, thus exhibiting the most various orders 

 grouped together, we yet discover very determinate laws in 

 the case of many individual groups of one and the same or- 

 ders. A single species of fossil, as Goniatites, Trilobites, or 

 Nummulites, sometimes constitutes whole mountains. Where 

 difierent families are blended together, a determinate succes- 

 sion of organisms has not only been observed with reference 

 to the superposition of the formations, but the association of 

 certain families and species has also been noticed in the lower 

 strata of the same formation. By his acute discovery of the 

 arrangement of the lobes of their chamber-sutures, Leopold 

 von Buch has been enabled to divide the innumerable quan- 

 tity of Ammonites into well-characterized families, and to 

 show that Ceratites appertain to the muschelkalk, Arietes to 

 the lias, and Goniatites to transition limestone and graywacke.§ 

 The lower limits of Belemnites are, in the keuper, covered by 

 Jura limestone, and their upper limits in the chalk forma- 

 tions. || It appears, from what we now know of this subject, 

 that the waters must have been inhabited at the same epoch, 

 and in the most widely-remote districts of the- world, by shell- 

 fish, which were, at any rate, in part, identical with the fossil 

 remains found in England. Leopold von Buch has discovered 

 exogyra and trigonia in the southern hemisphere (volcano of 



* Valenciennes, in the Comptes Rendus de V Acadimie des Sciences, t. 

 vii., 1838, Part ii., p. 580. 



t la the Weald clay; Beudant, Giologie, p. 173. The ornitholite* 

 increase in number in the gypsum of the tertiary formations. Cuvier 

 Ossemens Fossiles, t. ii., p. 302-328. 



t [Recent collections from the southern hemisphere show that this 

 distribution was not so universal during the earlier epochs as has gen- 

 erally been supposed. See papers by Darwin, Sharpe, Morris, and 

 M'Coy, in the Geological Journal.'] — Tr. 



$ Leop, von Buch, in the Abhandl. der Berl. Akad., 1830, s. 135-187 



II Quenstedt, Fldizgehirge Wnrfemhergs, 1843, s. 135. 



