36 msTOHv OF 



kind of free-stone, in which these petrified shells are found m 

 great abundance. This being the case, it may be conjectured, 

 as we have accounts of these pyramids among the earliest records 

 of mankind, and of their being built so long before the age of 



tribes, essential specific differences are perceived ; and these differences 

 become more striking as we recede from the latest formations. lo our cra^ 

 and fresli-water beds some species may be discovered which possess 

 a (strong similarity, if not absolute identity, with those living in our 

 lakes and seas. Even here, the identity is maintained but by a limit- 

 ed number, which are intermixed with numerous others that have 

 no recent analogues. Investigations in fossil conchology lead, therefore, 

 to one result ; that, with the inconsiderable exceptions that have been stat- 

 ed, the species have not been perpetuated to our times. 



One of the most remarkable facts elicited is, that certain Testacea, whose 

 genera were abundantly preserved and prolonged through so many forma- 

 tions, should now exist so sparingly, or be entirely lost. We might instance 

 the TerebratulsB, which abound no less in the mountain limestone than in 

 the chalk, and in almost every intermediate rock, which are absent in nearly 

 every one of our tertiary beds, and re-appear in the most recent. Not less 

 than 100 fossil species of Terebratulae, and myriads of individuals, are known 

 to us ; but the recent shells of this genus are comparatively few. Of Tri. 

 g'onia, also, 25 species are found in our strata, often abundantly, and termina- 

 ting, like the Ammonites, with the chalk. Until lately, thi.s genus was 

 considered to be extinct; but one species has been discovered on the shores 

 of New Holland. Of Ammonites, so profusely distributed, whose species 

 amount, it is said, to no less than 200, and of which about 175 are known iu 

 the English formations, none now remain. 29 species of Products, 3 of Pen. 

 tameriis, and 19 of Spirifer, inhabited the waters that produced the transi- 

 tion and mountain limestone, and contiguous shales ; but these genera are 

 altogether extinct. Indeed, almost the whole series of antediluvian nuilti. 

 locular shells seem to have shared a similar fate. On the other hand, instan- 

 ces are no less abundant and striking, where the recent species comprehend- 

 ed under certain genera do greatly outnumber the fossils. Thus, under the 

 liinnean genus Conus are comprised 155 species existing ; but only 3 occur 

 fossil in our London clay. The genus Cypraea contains about 110 living 

 species, and only four fossil in the tertiary beds. Thus, during the revolu- 

 tions of ages, some races have been extinguished, and have given place to 

 others which may still be traced in our seas. In the great tertiary deposits 

 of the Sub-Apenninea, Brocchi conceived he could point out some marine 

 Bhells, which are now very widely dispersed, in the Indian and American 

 Oceans, the Atlantic, the Red Sea, the Persian Gulf, and the coasts of Africa 

 and Jamacia. 



When we consider the enormous proportion of insects to the rest of tlie 

 animated beings in the present world, — being, according to Baron Humboldt, 

 no less than 44,000 out of 51,700, — we might expect to discover morn fre- 

 quent traces of these tribes in the fossil world. Whether they did not pro- 

 vail in such numbers during the former period of the globe, or whether, aa 

 is most probable, the extreme delicacy of theii- structure was unfavourable 

 to their preservation, we have only the fact, that but scanty traces of their 

 former existence, particularly in the elder beds, do now appear. 



