Flints of the Upper or White Chalk. 171 



less reverence than he regards the inference he could not deny 

 was based, at all events, on a due amount of analogical 

 reasoning. 



But this raises the very important question, whether the 

 Trimmingham chalk and flints can, for the purposes of the 

 present inquiry, with any propriety be ranked in the same cate- 

 gory as the typical chalk-strata, which have as certainly been 

 deposited at abyssal depths in the ocean as the Trimmingham 

 strata have been deposited in comparatively shallow water. 

 On this point I do not propose to offer an independent opinion, 

 but shall content myself with citing the opinions of experienced 

 geologists, and amongst others of Mr. Sollas himself. 



Referring, in the first section of his paper, published in the 

 'Annals' for November 1879 (which was really a treatise 

 upon the Trimmingham flint-spicules and nodules), to the 

 Sponges which furnished the still-existing spicules, he says 

 these " lived on a sea-floor probably somewhere between 100 

 and 400 fathoms deep." In the later (i. e. December) portion 

 of his paper bearing the same title, after noting the fact that 

 " currents have had some influence " in causing an addition 

 to the proper spicular complement " of the Trimmingham 

 forms from Sponges of other kinds," he again admits " the 

 flints " in this locality " were not formed at any abyssal 

 depth," but at from " 100 to 400 fathoms, giving a pressure 

 of from 20 to 80 atmospheres," by which he considers the 

 solution of the spicules in sea-water might have been 

 aided*. 



Now, according to the authorities on the subject about to 

 be cited, it will be seen that the average depth at which the 

 ancient Cretaceous mud was deposited is so vastly in excess 

 even of the maximum depth indicated for the Trimmingham 

 deposit, that the conditions under which animal life existed in 

 the two regions do not admit of comparison. In the one 

 region the water immediately overlying the sea-bed must have 

 been in a state of practically perfect quiescence ; in the other 

 (as collateral evidence, to be presently produced, will show), 

 the water immediately overlying the sea-bed must have been 

 in a state of constant and perhaps even powerful movement, 

 owing to tidal and other currents. In the one region, sponge- 

 life (the now admitted chief source of the silica from which the 

 chalk-flints were formed) was in all probability developed, as 

 it is known to be in our own day, to an enormous extent ; 

 and with it, of course, the dense protoplasmic environment 

 which forms an organic constituent of the deep-sea sponges, 

 ♦ Loc, cit. pp. 442, 444. 



