72 PAPERS, ETC. 



twenty-four inches), almost every iiich of clay seems to 

 have a shell peculiar to itself, not found higher or lower ; 

 the depositlon of such a minute part of the earth's crust 

 beiug the period during which a new species was intro- 

 duced, again to become extinct. For instance, the Leptoena 

 Mooren, with which is associated Leptcena Bouchardii, is 

 found only in the first inch, resting on the Maristone ; 

 the latter passes a little higher, and is then lost. Above 

 these is found a new species, and the smallest known Spi- 

 rifer — Spirifer Ibninsteriensis, which has its habitat, if I may 

 so speak, in a higher band of clay. These sheUs can only 

 be obtained by washing the beds — a process somewhat 

 siinilar to that pursued by the Australian gold seekers, but 

 unfortunately not so profitable. I mentioned that I had 

 found but one species of shell common to the beds of the 

 Middle and Upper Lias, that was a solitary specimen 

 of Spirifer rosfratus, which is as yet the last Spirifer. 



There is a remarkable persistence in the distribution of 

 organic remains, in beds of the same age, over large areas. 

 If a piece of clay were sent to me from bowever remote 

 a country, and it contained a single specimen of a species 

 of Leptcena identical with one in the Upper Lias, the con- 

 clusion would at ouce be arrived at, that the beds were 

 equivalents. Since these Brachiopods have been described, 

 they have been sought for on the continent ; and I have 

 lately been informed that M. Deslongchamp, an eminent 

 French geologist, has obtained them from beds in the 

 neighbom-hood of Caen, in Normandy, but associated 

 with some new forms not yet found here. I have also 

 heard that one of my species of Thecidea, a shell not so 

 large as a pea, has been obtained at the Kitzburg, in the 

 Austrian Alps. 



In a paper such as the present, it is impossible to notice 



