MICRO-ORGANISMS. 769 



this view has lately been substantiated by the deep-sea investiga- 

 tions of English naturalists. Wyville Thomson says : " There can 

 be no doubt whatever that we have forming at the bottom of the 

 present ocean a vast sheet of rock which very closely resembles chalk ; 

 and there can be as little doubt that the old chalk, the Cretaceous for- 

 mation, which in some parts of England has been subjected to enor- 

 mous denudation, and which is overlaid by the beds of the Tertiary 

 series, was produced in the same manner and under closely similar 

 circumstances " ; and he also thinks it is " probable that in the deeper 

 parts of the Atlantic a deposit, differing possibly from time to time in 

 composition, but always of the same general character, might have 

 been accumulating continuously from the Cretaceous, or even earlier 

 periods, to the present day." * What enormous swarms and succes- 

 sive generations of rhizopods have existed, to effect such amazing re- 

 sults ! Were all the extinct chalk animals resurrected at once, they 

 would envelop the earth as did the primitive waters before the land 

 was apart from the sea ; we should have an ocean of protoplasm filled 

 with their shells. Figuier truly says : " With these microscopic ani- 

 mals Nature has worked wonders in geological times ; nor have those 

 wonders ceased in our days." 



Their diminutive size, marvelous reproductive capacity, and tena- 

 city of life, together with the readiness with which they adapt them- 

 selves to new and various conditions of existence, not only have in- 

 sured them a wide distribution in space, but also have enabled them to 

 survive the destructive causes which exterminated higher forms through 

 long and successive ages of geological time. Among about one hun- 

 dred and twenty-five kinds (genera) of shelled, root-footed animals, 

 only about fifteen are not fossil. Of the one hundred and ten species 

 of those with perforated shells now living in the Atlantic chalk-ooze, 

 the number of species common to it and the various geological forma- 

 tions in England is estimated as fifty-three with the crag, twenty- 

 eight with the London clay, nineteen with the chalk, seven with the 

 Rhsetic and Upper Trias, one with the Permian, and one with the Car- 

 boniferous. The survival of so many species in the group is a strik- 

 ing testimony against the theory that the species of each geological 

 division of time ended in a totally demolishing and exterminating 

 catastrophe. The links in their chain are small but numerous, contin- 

 uously uniting the organic life of remote ages with that of to-day. 



At present the immense numbers of their shells on some shores is 

 remarkable ; indeed, the sands of some localities are largely composed 

 of them. D'Orbigny obtained 3,800,000 porous shells from a single 

 ounce of sand on the shores of the Antilles. According to Soldani, 

 one ounce of sand from Rimini, on the Adriatic, yields 6,000 shells. 

 This scientist described and figured a great number of these in Italy, 

 publishing an elaborate folio work with 228 copperplate illustrations, 



* " Depths of the Sea," p. 470. 

 vol. xv. 49 



