, Conchology. 101 



may take place sometimes by the centre of the crater of ele- 

 vation, sometimes by neighboring points. 



Though it is difficult, from the meagre details hitherto ob- 

 tained, to form any correct opinion of the minerological char- 

 acter of the upraised mass, yet there is nothing in those details 

 to warrant the supposition that there is no stability or perma- 

 nence in the composition of the island. The pulverized re- 

 mains of coal deprived of its bitumen, the hard scorice, dense 

 and sonorous (phonolites?) the amorphous rocks with metallic 

 lustre and ironstone clay, would appear to associate the 

 eruption with the rocks of the carboniferous series — an opin- 

 ion which receives additional probability from the ejection of 

 unchanged pieces of limestone ; as we see, between Pettycur 

 and Bruntisland in Fifeshire, beds of limestone and of non- 

 bituminous coal elevated by rocks of plutonic origin, and 

 argillaceous and argillo-calcareous rocks changed into leu- 

 costines and spilites. — Magazine of Natural History. 



Note. — The last account of this island states that it exists no more 

 since the 20th of December last, when it sunk at the time of a violent 

 earthquake. At the place whei-e it was situated there now remains a 

 kind of rock covered with a shallow depth of water. Ed. 



CONCHOLOGY. 



NO. II. 



Of the Constituent Parts of Shells. The nature 

 and component parts of testaceous substances have been 

 particularly investigated by Mr. Hatchett, from whose paper 

 we extract the following observations. 



In his examination of marine shells, Mr. Hatchett found, 

 from the nature of the substance of which they are composed, 

 that they might be arranged in two divisions. 



Under the first are included those which have a porcellaneous 

 appearance and enamelled surface, and exhibit, when broken, 

 something of a fibrous texture. The other division is 

 distinguished, by having a strong epidermis or covering, under 

 which is the shell, composed principally or entirely of mother 

 of pearl. To the first division belong different species of 

 voluta, cyprsea, and others. The second comprehends the 

 oyster, the river muscle, and some species of haliotis and 

 turbo. 



Porcellaneous Shells. The shells of this description 



