234 



Order of Arrangement of Shells in the different Forma- 

 tions. — It has been conjectured by some naturalists who had 

 become convinced of the comparatively late creation of land 

 animals and of man, that the peopling of this planet had 

 commenced, in the enduing with the principles of life, beings 

 of the simplest forms and organization ; and, that by the 

 influence of certain external causes, acting through passing 

 ages, those changes had been gradually wrought in succeed- 

 ing animals, from which have resulted the numerous differ- 

 ences which constitute the various tribes : rising from the 

 almost lifeless sponge to the highly complex and more per- 

 fect animal, man. On this hypothesis it might have been 

 expected that those beings which had possessed life under 

 its most simple modifications, would be found in the earliest 

 formed strata ; and that, in proportion to the lateness of 

 the period at which the strata had been formed, would be 

 the degree of complexity in the organization of the inha- 

 bitants whose remains they would contain. But investi- 

 gation has ascertained, and the preceding table manifests 

 most decidedly, at least, with respect to the class of animals 

 of which we are now treating, that such a conjecture is ill 

 founded. In the carboniferous and the mountain limestone 

 are the remains of shells of the earliest creation, which are 

 unexpectedly found, with hardly an exception, to exceed, 

 in complexity of structure, all the shells which have been 

 discovered, either in any subsequent formation, or living in 

 our present seas. It is in this early creation that those 

 shells are found which possess that complicated structure, 

 very rarely found in the shells of this day, which enabled 

 their inhabitants to rise and sink with them in the water. 

 Such are the many-chambered univalves, the nautilus, cun- 

 monites, orthoceratites, cv:c. The bivalves and multivalves of 

 that era also seem to have been endued with a similar pro- 

 perty. The curious structure of spirifer, PI. vii. fig. 15, 

 and the multilocular construction of prodvctu^ of Martin, 



