MINUTE ORGANISMS AS ROCK-MAKERS 1085 



kalk of Europe. They have also been identified in rocks of Secondary 

 and even of Palaeozoic age. It is an admitted rule in geological 

 science that the past history of the earth is to be interpreted, so far 

 as may be found possible, by the study of the changes which are 

 still going on. Thus, when we meet with an extensive stratum of 

 fossilised Diatomacece in what is now dry land, we can entertain no 

 doubt that this silicious deposit originally accumulated either at the 

 bottom of a fresh-water lake or beneath the waters of the ocean ; 

 just as such deposits are formed at the present time by the produc- 

 tion and death of successive generations of these bodies, whose 

 indestructible casings accumulate in the lapse of ages, so as to form 

 layers whose thickness is only limited by the time during which 

 this process has been in action. In like manner, when we meet 

 with a limestone rock entirely composed of the calcareous shells of 

 Foraniinifera. some of them entire, othei's broken up into minute 

 particles (as in the case of the Fasulina limestone of the Carboni- 

 ferous period, and the Xnnmn/Titie limestone of the Eocene), we 

 interpret the phenomenon by the fact that the dredgings obtained 

 from certain parts of the ocean-bottom consist almost entirely of 

 remains of existing Foraminifera, in which entire shells, the animals 

 of which may be yet alive, are mingled with the debris of others 

 that have been reduced to a fragmentary state. Such a deposit, 

 consisting chiefly of Orbitolites, is at present in process of formation 

 on certain parts of the shores of Australia, as Dr. Carpenter was 

 informed by Mr. J. Beete Jukes, thus affording the exact parallel to 

 the stratum of Orbltolites (belonging, as his own investigations have 

 led him to believe, to the very same species) that forms part of the 

 ' calcaire grossier ' of the Paris basin. So in the fine white mud 

 which is brought up from almost every part of the sea-bottom of the 

 Levant, where it forms a stratum that is continually undergoing a 

 slow but steady increase in thickness, the microscopic researches of 

 Professor W. C. Williamson 1 have shown, not only that it contains 

 multitudes of minute remains of living organisms, both animal and 

 vegetable, but that it is entirely or almost wholly composed of such 

 remains. Amongst these are about twenty-six species of "Dia- 

 tomacea? (silicious), eight species of Foraminifera (calcareous), and a 

 miscellaneous group of objects (fig. 810). consisting of calcareous and 

 silicious spicules of sponges and G'orgot/iir. and fragments of the 

 calcareous skeletons of echinoderms and molluscs. A collection of 

 forms strongly resembling that of the Levant mud, with the exception 

 of the silicious Diatomacese, is found in many parts of the 'calcaire 

 grossier' of the Paris basin, as well as in other extensive deposits of 

 the same early Tertiary period. 



It is, however, in regard to the great chalk formation that the 

 information afforded by the microscope has been most valuable. 

 Mention has already been made of the fact that a large proportion 

 of the North Atlantic sea-bed has been found to be covered with an 

 ' ooze ' chiefly formed of the shells of Globigerince ; and this fact, first 

 determined by the examination of the small quantities brought, up 

 by the sounding apparatus, has been fully confirmed by the results of 



1 Memoirs of the Manchester Litcranj and Philosophical Society, vol. vii. 



