1 2 Mr. J. S. Bowerbank on Moss Agates 



broken, and presenting appearances of much confusion and 

 disarrangement, as at a, a, fig. 2, and no remains of the struc- 

 ture surrounding them are perceptible. But in some few por- 

 tions, and especially near the margin where the perfect sponge- 

 tubes are found, we perceive each of these red fibres to be en- 

 veloped by the semipellucid and horny-looking substance of 

 the sponge, as seen in the centre of PL I. fig. 2, thus proving 

 that the red fibre is in reality the cast of the interior of the 

 tubular sponge fibre ; and if we compare them with the hol- 

 low spaces of the perfect tubes, we find them to be as nearly 

 as possible of the same diameter. 



In the portion of the agate represented by PL I. fig. 2, 

 there are parts of the tissue seen at b, b, b, into which the red 

 pigment does not appear to have entered, and when the fibre 

 is in the most perfect state of preservation this is usually the 

 condition in which it is found ; and it is natural that such 

 should be the case ; for in the recent type of these sponges, 

 Spongia Jistularis, it is always found, that although the inter- 

 nal cavity is continuous throughout the whole of the fibrous 

 structure, yet that it is universally closed at a short distance 

 before it arrives at the natural termination of a fibre. 



In another specimen, which is in my possession, of a moss 

 agate from Oberstein, we have the spongeous structure in a 

 different form. In the first specimen described the most 

 striking feature is the bright red fibrous-looking casts of the 

 interior of the sponge-tubes ; while, in this, we have in the 

 best preserved parts of the structure the walls of the tubes 

 themselves impregnated with the red pigment and the inte- 

 rior of the tubes filled with pellucid silex ; while in that por- 

 tion which has suffered most by decomposition, there is a con- 

 fused mass of bright red with obscure traces of fibrous struc- 

 ture, with here and there a fibre in a sufficiently good state of 

 preservation to enable us to recognise the whole as the same 

 substance as the more perfect structure, but so obscured by 

 decomposition as to render it perfectly undistinguishable from 

 inorganic and extraneous matter, if it were not for the better 

 state of preservation of other parts of the sponge. 



Another agate which I examined I found to be, literally 

 speaking, a complete mass of sponge. The fibre of the centre 

 of this specimen, for about one-third of its diameter, is of a 

 bright red colour, the surrounding part is of an ochreous yel- 

 low, but the organized structure does not vary in any respect 

 but in colour. There are the casts of a few small foraminated 

 shells dispersed amid the spongeous tissue, and in a few irre- 

 gular cavities which occur in it I observed that the silex was 

 arranged in that peculiar stratified mode which stamps it as 

 an agate. In the fourth agate examined, the sponge-tubes 



