266 PALEONTOLOGY: FOSSIL ORGANIC REMAINS. 



highly organised cephalopodes and crustaceans, so that 

 widely different orders of this part of the animal kingdom 

 appear intermingled ; there are, nevertheless, many isolated 

 groups belonging to the same order, in which determinate 

 laws are discoverable. Whole mountains are sometimes found 

 to consist of a single species of fossil, goniatites, . trilobites, 

 or nummulites. Where different genera are intermingled, 

 there often exists a systematic relation between the series of 

 organic forms and the superposition of the formations ; and 

 it has been remarked, that the association of certain families 

 and species follows a regular law in the superposed strata 

 of which the whole constitute one formation. Thus Leo- 

 pold von Buch, after classifying the immense variety of 

 ammonites in well defined families by observing the dispo- 

 sition of the lobes, has shewn that the ceratites belong to 

 the muschelkalk, the arietes to the lias, and the goniatites 

 to the transition limestone and older rocks. ( 311 ) Belem- 

 mtes have their lower limit ( 312 ) in the keuper sandstone, 

 below the Jura or oolitic limestone, and their upper limit in 

 the chalk. It has been found that the waters in the most 

 distant parts of the globe were inhabited at the same epochs 

 by testaceous animals corresponding at least in generic 

 character with European fossils: for example, Von Buch 

 has described species of exogyra and trigonia from the 

 southern hemisphere (from the volcano of Maypo in Chili), 

 and D'Orbigny has indicated species of ammonites and 

 gryphsea from the Himalaya and the Indian plains of Cutch, 

 which have been supposed even specifically identical with 

 those of the ancient oolitic beds of Prance and Germany. 



Strata defined by their fossil contents, 01 by the frag- 

 ments of other rocks which they include, form a geological 



