630 



MICROSCOPIC GEOLOGY. 



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

 of fossilized Diatom.acece ( 191) in what is now dry land, we can 

 entertain no doubt that this siliceous deposit originally accumu- 

 lated either at the bottom of a fresh-water lake, or beneath the 

 waters of the ocean ; just as such deposits are formed at the pre- 

 sent time, by the production and death of successive genera- 

 tions 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 

 ( 190). In like manner, when we meet with a limestone-rock 



entirely composed of the 



FlG - 334 - calcareous shells of Fora- 



minifera, some of them 

 entire, others broken up 

 into minute particles, we 

 interpret the phenomenon 

 by the fact, that the dredg- 

 ings obtained from certain 

 parts of the ocean-bottom 

 consists almost entirely of 

 remains of existing Fora- 

 minifera, in which entire 

 shells, the animals of 

 which may be yet alive, 

 are mingled with the 

 debris of others that 

 have been reduced by 

 the action of the waves 

 to a fragmentary 

 state. 1 Now 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 con- 

 tinually undergoing a 

 slow but steady in- 

 crease in thickness, 

 the microscopic re- 

 searches of Prof. "Wil- 

 liamson 2 have shown 

 that not only are there 

 multitudes of minute 

 remains of living or- 



1 Such a deposit, consisting chiefly of Orbitolites ( 287) is at present in the act of 

 formation on certain parts of the shores of Australia, as the Author is informed by Mr. 

 J. Beete Jukes; thus affording the exact parallel to the stratum of Orbitolites (belonging, 

 as the Author's investigations have led him to believe, to the very same species) that 

 forms part of the " Calcaire Grossier" of the Paris basin. 



2 " Memoirs of the Manchester Literary and Philosophical Society," vol. viii. 



Microscopic Organisms in Levant Mud : A, D, siliceous spi- 

 cules of Tethya; B, H, spicules of Geodia ; c, Sponge-spicule 

 (unknown); E, calcareous spicule of Grantia / F, G, M, o, por- 

 tions of calcareous skeleton of Echinodermata; H, I, calcareous 

 spicule of Gorgonia ; K, L, N, siliceous spicules of Halichondria ; 

 P, portion of prismatic layer of shell of Pinna. 



