PALEONTOLOGY. 279 



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

 mulites. sometimes constitutes whole mountains. Where dif- 

 ferent families are blended together, a determinate succession 

 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 arrange- 

 ment of the lobes of their chamber-sutures, Leopold von Buch 

 has been enabled to divide the innumerable quantity of Am- 

 monites into well characterised families, and to show that 

 Ceratites appertain to the muschelkalk, Arietes to the lias, and 

 Goniatites to transition limestone and greywacke.* The lowei 

 limits of Belemnites are, in the keuper, covered by Jura lime- 

 stone, and their upper limits in the chalk formations, f 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 

 Maypo in Chili), and d'Orbigny has described Ammonites 

 and Gryphites from the Himalaya and the Indian plains of 

 Cutch ; these remains being identical with those found in the 

 old Jurassic sea of Germany and France. 



The strata which are distinguished by definite kinds of petri- 

 factions, or by the fragments contained within them, form a 

 geognostic horizon, by which the enquirer may guide his steps, 

 and arrive at certain conclusions regarding the identity or 

 relative age of the formations, the periodic recurrence of cer- 

 tain strata, their parallelism or their total suppression. If 

 we classify the type of the sedimentary structures in the 

 simplest mode of generalization, we arrive at the following 

 series in proceeding from below upwards. 



1. The so-called transition rocks, in the two divisions of 

 upper and lower greywacke (silurian and devonian systems), 

 the latter being formerly designated as old red sandstone. 



2. The lower trias,% comprising mountain limestone, coal- 



* Leop. von Buch, in the Abliundl. der BerL Akad., 1830, a. 135- 

 187. 



t Quenstedt, Fldzgebirge Wvirtemberys, 1843, 8. 135 

 t loid a. 13. 



