Scleidifc Intdlhj ncc — Mineraloqy and Chemidrif. 187 



Greenougli had positively ascoi-tained the action of the HeUx aspersa 

 on limestone. 



To the facts above narrated, and the authorities just cited, M. 

 Constant Prevost adds a circumstance which appears to him to con- 

 firm his first idea, and to render it unquestionable that the Helices 

 have themselves scooped out the long canals at the bottom of which 

 we find them. He pointed out the fact, in one of the specimens 

 presented to the Society, that the bottom of one of the largest ca- 

 vities presented an exact counterpart to the form of the Helix which 

 lodged in it : a small projection corresponds exactly to the depres- 

 sion at the origin of the column, and, by taking an impression of the 

 cavity in plaster, he obtained a relief which in no respect differed 

 from that of the base of the shell. 



The Helix found at Boulogne-sur-mer was the common H. aspersa. 

 That observed at Monte Pelegrino seemed to be a very remarkable 

 variety of that species, at least it is so regarded by Kosmaesler, who 

 has figured it under that name in his Iconographia uf Land and 

 Fresh-water Shells, pi. xxii. It is the Helix described and figured 

 as distinct, under the name oi' li lix Mazzv.U by Zau and Phillipi, 

 and under that of//. Rtinujis by Mcnkc. 



The same Helix, now found alive in the vicinity uf Palermo, i.s 

 met with in a fossil state in the marine tertiary deposits which 

 surround the base of Monte Pelegrino. M. Constant Prevost further 

 remaikfid, that it is by maceration, or by chemical action, and not by 

 a mechanical action, that the Helix corrodes the stone. In fact, the 

 compact limestone of Monte Pelegrino, which is a little argillaceous 

 and bituminous, is traversed in every direction by numerous veins of 

 crystalline limestone ; these more resisting parts are seen projecting 

 like a kind of net-work on the interior walls of the cavities, which 

 could not have taken place if the calcareous matter had been re- 

 moved by friction. 



M. Constant Prevost terminates his communication by shewing 

 how important it is that geologists should not confound the perfora- 

 tions which may have been produced in rocks by marine molluscs 

 with those of Helices, since the former, observed at the present time 

 on very elevated parts of continents, indicate ancient levels of the 

 sea, or the relative elevations of the ground, whereas the perforations 

 of the Ilelex indicate nothing of that nature. — From Ijinstituf., 

 April 1842, p. 132. 



26. On the residuum of the Combustion of the Diamond, b>/ M. 

 Pcizhoyt. — By repeating the experiments of Messrs Dumas and 

 Stass, in order to determine the atomic weight 'if carbon by the cum- 



