18 MICROSCOPIC GEOLOGY. 



covered with, if it does not in great part consist of, these infi- 

 nitesimal structures. And Professor Baily, who has carefully 

 examined the soundings brought up from this sub-oceanic table- 

 land, states that they consist entirely of microscopic shells, with- 

 out a particle of sand or gravel, and that with the exception of a 

 small number of the silicious shells of the Diatomacese, the 

 entire mass of the soundings consisted of the perfect calcareous 

 shells of the Foraminifera ; a fact which is all the more remark- 

 able from the striking contrast it presents to the deep-sea sound- 

 ings from the Pacific, before referred to, which are chiefly made 

 up of the silicious shields of the Diatomacese. 



But this is not all. In former epochs of the earth's history 

 the Foraminifera existed in even greater profusion than at present : 

 and their remains form the principal constituent of some import- 

 ant geological formations. In many of the tertiary strata they 

 occur in the greatest abundance. " It may even be asserted," 

 says Professor Ansted, " that the capital of France, as well as 

 the towns and villages of the neighbouring department, are 

 almost entirely built of Foraminifera." But it is in the chalk 

 more especially that these minute shells chiefly abound ; recent 

 observations having shown that this material is everywhere, 

 in great part, and in several districts almost wholly, composed 

 of them, either still perfect, or nearly so, or else broken and 

 ground down to a fine powder. Now, let the reader make an 

 effort to realize this fact in respect to the chalk formation, as it 

 is developed in England alone. Let it be remembered that this 

 material occurs over nearly the whole of the south-eastern part 

 of the island, and that in many places it has a thickness of 

 several hundred feet, and then let the reader form an estimate, 

 if he can, of the number of these fragile and delicate shells which 

 lie buried within our far-extending ranges of chalk hills. 



But turning from these vast accumulations of the microscopic 

 life of the ocean of the chalk epoch, let us come back again to 

 our own ponds and ditches, and to the living wonders with which 

 they abound. 



One can hardly characterize as " pets " creatures so exces- 

 sively minute as those with which we are now concerned ; but 

 if there be any one of the number which more than another 

 deserves the name, it is, undoubtedly, the " Bell Animalcule " 

 ( Vorticella), a prime favourite with every owner of a microscope, 



