Dr. Mac Culloch on the Geology of Gleti Tilt. 319 



although on a first glance strongly resembling its more friable 

 varieties. It is soluble without residuum in muriatic acid. On a 

 narrow inspection it is found to contain minute fragments of shells, 

 particularly towards the surface, while deeper in the bed all marks 

 of organization disappear. It is also every where penetrated by the 

 fibrous roots of grasses and other plants, or by the minute channels 

 which their decay has left. It does not acquire any induration on 

 drying, as the specimens before the Society will show. On the 

 immediate surface, or at small depths where the decomposing causes 

 have had less time to act, entire shells are found, and numbers of 

 these may be collected in a very perfect state. Among those which 

 Idid collect I only found the following in a state sufficiently entire 

 for examination. 



No. 1. Helix arbustorum. 



2. Appears to be Helix rufescens, or hispida, 



3. Two broken specimens, of which I cannot speak with 



the least decision. 



4. I conjecture it to be Helix fusca of Montagu j and perhaps 



it agrees with Draparnaud's genus Vitrine. 



5. A small Planorbis j but of what species I am unable to 



determine. 



6. Appears to be a minute Lymneus ; perhaps Lymneus 



minutus of Braard. 



All appear to be terrestrial shells. 



This then is, to be considered as a land formation of calcareous 

 matter, if we may use such a term, and the result of the successive 

 renewal and death of these minute animals for a length of time 

 unknown. Whether this process is still going on I was unable 

 to discover. After much search I did not find any living animal, 

 but among the helices were some with their colours so perfect, 



