Geology. 



415 



II. GEOLOGY. 



1. On the Spongeous Origin of the Siliceous Bodies of the Chalk 

 Formation; by J. S. Bowerbank, (Proc. Brit. Assoc., August, 1856; 

 Ath. No. 1505.) — The author attributes the whole of the numerous strata 

 of nodular and tabular flints to vast quantities of spongeous bodies that 

 existed in the seas of those remote periods. The elective attraction of the 

 animal matter of the sponges inducing the deposit of the silex, which 

 in the first instance is always in the form of a thin film surrounding the 

 skeleton of the sponge, and from which successive crops of calcedonic 

 crystals proceed, until the solidification of the whole is effected. The 

 tabular form is accounted for on the presumption that the sponges origin- 

 ating the deposit grew on a more consolidated bottom than the tuberous 

 ones, and that they therefore developed themselves in a lateral direction 

 instead of in an erect position, and on approximating each other were 

 cemented together, and thus formed continuous beds of considerable ex- 

 tent ; and the author illustrated this portion of his subject by the produc- 

 tion of four recent sponges of the same species, which, by being placed 

 in contact while in the living state, became firmly united to each other 

 within eighteen hours, ultimately forming one sponge. The occurrence 

 of the shells of Echinoderms and of bivalve shells filled with flint was 

 accounted for on the same principle ; and the author produced recent bi- 

 valve shells, in a closed condition, completely filled with recent sponges of 

 the same species as the sponges of commerce. The loose specimens of 

 fossil sponges included in the Wiltshire flints were explained on the prin- 

 ciple that, although sponges of the same species readily adhere to each 

 other when placed in contact, those of different species never unite, how- 

 ever closely they may be pressed together. The author concluded his 

 paper by applying the same principles to the siliceous deposits of the 

 whole of the geological formations which were of aqueous origin. 



2. On some Palaeozoic Starfishes, compared with Living Forms ; by 

 J. W. Salter, (Proc. Brit. Assoc., August, 1856 ; Ath. No. 1505.) — The 

 object of the communication was chiefly to exhibit some new forms of 

 Asteriadse, from the Upper Silurian rocks, which have all .the aspect of 

 Ophiuridse, but are essentially distinguished by the number of ossicles 

 which go to form a single segment of the arms, — the lower surface show- 

 ing the characteristic double row of ambulacral bones (in this case flat 

 plates,) and the upper being composed either of two or more rows of 

 plates, while the Ophiuridse have a single plate above, and one below. 

 There is, however, the closest similarity to the latter family in the length 

 of the arms and the restriction of the disc (Protaster, Forbes), as well as 

 in the great length of the spines on the margin (Palceocoma), while in 

 the pentagonal form and simply plated integument of another s;enus 

 (Palasterina), there is a much nearer approach made to the Asteriscus or 

 Palmipes roseus than to any other type of living starfish. It is to this 

 group that the fossils are supposed to belong ; and to some of the species 

 which have the disc little developed, or quite absent, there is a strong re- 

 semblance in a Lower Silurian form originally described by Forbes as 

 Ur -aster, but which better specimens show to have had but two rows of 

 suckers, and the avenues bordered by very large plates. The name Pa- 



