THE SUCCESSION OF MOLLUSCA. 93 



cephalopods, ere long destined to be dismissed from among 

 the workers which were operating so assiduously to fit this 

 globe for man's tenancy, " seem to have expanded into a 

 vast multitude of strange forms before becoming finally ex- 

 tinct." — We step on into the modern epoch; and there, too, 

 the mollusca accompany us — different, indeed, in species from 

 all that had preceded them, but alike in this work of contri- 

 bution to our earth's perfection. The Ammonites have died 

 out, and their place and purpose is occupied and fulfilled 

 by carnivorous gasteropods, in their spiral shells, created 

 in the most remarkable profusion. The Nummulites — small 

 shells of doubtful classification — also abound, and are so 

 incredibly multitudinous in some localities that rocks are 

 made up of them. " Other smaller foraminiferous shells 

 have built great masses of the limestone of this period." 

 They enter so largely into the composition of the stones of 

 which Paris is built, that it may be said without exaggeration 

 that that great city is built of shells. *- — This very general 

 statement is sufficient for the purpose in view, of indicating 

 the vast influence the mollusca have had in their capacity as 

 assistant-architects of our world ; but to make their remains 

 subservient to geology, the conchologist has to go more nar- 

 rowly to work, — he has to ascertain the species which occur 

 in every layer, if I may so speak, of every strata; to mark 

 those which are peculiar to each ; to note the variations they 

 have undergone in their transition from one formation to 

 another ; the times of their creation — of their chief predomin- 

 ance — of their decay and extinction ; and to specify what 

 new forms come to supply the place of those which are about 

 to disappear, or which have been erased from the volume 

 of living entities. From such researches, which have been 

 conducted with a zeal and ability that cannot be too highly 

 praised, geologists have borrowed largely ; and though the 

 value of the evidence which fossil shells afford in unravelling 

 the mutations of the earth is variously estimated, yet it 

 seems agreed on all hands that it would be as wise for the 

 historian in tracing the history and manners of an ancient 

 people to neglect their medals and their monuments, as for 

 the geologist to overlook the light thrown over his antiqua- 

 rian researches by these medals of the ancient world. " The 

 different series of formations," says the Rev. Mr. Conybeare, 

 " differ very materially in the species of organic remains 

 which they include, and by which they are, therefore, said 

 to be characterised. The species frequently vary from form- 



* Desc. de Coq car. des Terrains, 253.— Dr. J. P. Smith's Script. Geol. 98. 



