EECEEATIVE SCIENCE. 



203 



beautiful tracery is easily revealed on thin 

 laminae, by the aid of a moderate glass. But 

 these sponges permeate the very flint itself, 

 are preserved in flint, and only manifest 

 themselves under peculiar circumstances. 

 But here we have a nodule of flint, with an 

 internal chamber, the nidus of a delicate 

 fruit-like body, which we regard as a fossil 

 sponge. It is in what is termed the upper 

 chalk deposit that flints abound. Oftentimes 

 we see them laid in courses at regular inter- 

 vals, as if the skilful hand of the mason had 

 arranged them. Examples of this kind occur 

 in the Isle of Wight.* Such, however, is 

 not the case as regards the chalk-cliffs on 

 the Kentish side of the sea, along or below 

 the estuary of the Thames. In these clifis 

 we find delicate shells and echinoderms (some 

 filled with chalk, others a solid mass of flint), 

 irregularly scattered, with occasional ammo- 

 nites ; while in the chalk pits near Graves- 

 end, we have, in addition, silicified sharks' 

 teeth and various other relics, including the 

 spines of echinoderms, and corals in abun- 

 dance. 



Let us then suppose our flint nodule to 

 have proceeded from this upper chalk depo- 

 sit, and then comes a question — Where was 

 it, and from what did it hang, when the fluid 

 or semifluid silex enveloped itP Was it a 

 tenant of some rift in the chalk-rock itself? 

 Are the silicified sponges in their primitive 

 seat ? It cannot be. There has been destruc- 

 tion, there has been a turmoil and melee; 

 then a quiet subsidence, a gradual deposit of 

 chalk through a series of ages, an infiltration 

 of fluid silex — there filling up echinoderms, 

 there inclosing sponges, there impregnating 

 the teeth of sharks and other fishes, and 

 there simply consolidating into masses which 

 give no trace of organic existence. 



We need not say that the great deposit of 

 chalk took place by degrees at the bottom of 

 a deep sea, nor shall we here analyze the 



* The arched rock in Scratchell's Bay. 



chalk itself; far too wide would the field be 

 for our prescribed limits j we pass the sxib- 

 ject by. 



To revert to our specimen : How happens 

 it that the flint has not tightly embraced the 

 kernel-sponge, but has left, as far as we can 

 probe, an interval, so as to form a chamber, 

 in which, except at the stalk, it seems to 

 remain free P Did the living gelatinous in- 

 vestment of the sponge once fill up the 

 vacuum, and then perishing, waste to a mere 

 nothing P Conjecture fails us. 



We have not broken the kernel, the gray* 

 tinted, granular superficies of which, with 

 the diverging fibrous lines, our sketch accu« 

 rately depicts, and therefore cannot positively 

 assert that its interior is purely silicious ; wo 

 presume, however, that such is the case, and 

 should be sorry to see it tested by experi- 

 ment. 



W. C. L. Martin. 



MOSSES IN FEEN-CASES AND 

 AQUAEIA. 



Mosses, properly selected, would form most 

 valuable, as well as attractive objects in the 

 fern-case and aquarium. In the former, 

 especially, Bryum pyreforme would thrive 

 most luxuriantly, and is valuable to use as a 

 surfacing to plants in pots, or even among 

 ferns in the open air, as it prevents the sur- 

 face of the mould from drying, and its root 

 are not strong enough to rob the plant. 



In the aquarium many would flourish, as 

 Fontinalis antipyretica, Cinclidotas fontin- 

 aloides, Hypnum ruscifolium, filicinum, 

 fluitans, riparium, and Bryum punctatum ; 

 and the following most lovely species are 

 worth a trial : Hypnum alopecurum and den- 

 droides, Bryum hornum, roseum, and ligula^ 

 turn ; the latter will most decidedly retain 

 their beauty for some time if they do not 

 vegetate. P. Y. B. 



