56 Medico- Botanical Society. 



in Hampshire is described. The subjects of chief interest with 

 regard to the shell marl are, its slow growth, tlie small pro- 

 portion of fuU-grow^n shells which are found in it in Forfar- 

 shire, the greater rapidity of its growth in the vicinity of springs, 

 its abundance in a part of Scotland in which limestone is very 

 rare, and its scarcity in the calcareous districts of England. 



The question is then considered, whether the shell marl be 

 exclusively derived from the exuviag of testacea, and the va- 

 rious arguments for and against this hypothesis are entered 

 into. 



In conclusion, Mr. Lyell takes a general view of the analogy 

 between the ancient and modern freshwater formations. 



Both of these may be described generally as consisting of 

 thin beds of calcareous, argillaceous, and arenaceous marls, 

 together with strata of sand and clay, to which the consoli- 

 dated beds bear upon the whole but a small proportion. 



The shells and plants contained in both are referable to the 

 same genera. 



The bones and skeletons of quadrupeds are found buried 

 at various depths in the marls of Forfarshire, as they occur in 

 the lower freshwater formation of Paris. 



Of the four desiderata mentioned by Messrs. Cuvier and 

 Brongniart (Essay on the Environs of Paris, p. 56), as being 

 requisite to complete the analogy between the deposits of lakes 

 now existing and those of a former world, three are supplied 

 by the lakes in Forfarshire: viz. 1. a compact limestone; 

 2. vegetables converted into the substance of their calcareous 

 matrix; 3. large beds of yellowish white calcareous marl. 



The rock marl of Forfarshire closely resembles the Traves- 

 tino of Italy, part of wliich is a recent formation, but part hais 

 been proved by M. Brongniart to be of a date probably as 

 ancient as the upper freshwater strata at Paris. 



The only difference remaining between the ancient and the 

 modern freshwater formations is, 1. the absence in the latter 

 of silex, which is only known as a modern deposit from water 

 connected with volcanic agency; and 2. the small scale on 

 which the recent accumulations proceed. 



If these differences are ascribable to a higher temperature 

 prevailing where the ancient freshwater rocks were formed, 

 they may perhaps disappear when the hitherto unexplored 

 tropical regions of the globe are fully investigated. 



MEDICO-BOTANICAL SOCIETY. 



At a meeting of this Society holden on Friday the l+th in- 

 stant, the Professor delivered a lecture upon a new essential 

 oil lately introduced from South America. It is called the Es- 



