138 Zoological Proceedings of Societies. 



in the soft shell marl, and are all still living in the waters on the 

 spot. Among the plants are the stems and seed vessels of Chares, 

 the latter being fossilized in such a manner as to present a perfect 

 analogy to the Gyrogonite of the ancient fresh-water formations. 



Mr. Lyell then considers the probable origin of the rock marl, 

 which appears to be derived from subjacent shell marl, through 

 which springs ascend, charged with carbonic acid. 



Some remarks are next offered on the shell marl of Forfarshire, 

 and some which the author has examined near Romsey, in Hamp- 

 shire, is described. The subjects of chief interest with regard to the 

 shell marl are, its slow growth, the small proportion of full grown 

 shells which are found in it in Forfarshire, the greater rapidity 

 of its growth in the vicinity of springs, its abundcince in a part of 

 Scotland in which limestone is \ery rare, and its scarcity in the 

 calcareous districts of England. 



The question is then considered whether the shell marl be ex- 

 clusively derived from the exuviae of testacea, and the various 

 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 fresh-water formations. 



Both of these may be described, generally, as consisting of thin 

 beds of calcareous, argillaceous, and arenaceous rnarls, together 

 with strata of sand and clay, to which the consolidated 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 fresh-water formation of Paris. 



Of the four desiderata mentioned by Messrs. Guvier and Brong- 

 niart, (Ess. on the Env. 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 Travertino 

 fof Italy, part of which is a recent formation, but part has been 



