Geological Society. 137 



larva which could be detected in it was that of a dipterous insect, 

 Mr. W. S. MacLeay stated it as his opinion, that this could not 

 be the cause of the damage | but that the injury having been pro- 

 duced by some coleopterous larva, or other cause, the juices of the 

 tree had flowed through the wound, and become putrescent, thus 

 aflbrding a nidus for the dipterous larva discovered. 



A portion of a " Catalogue of the New Holland Birds in the 

 collection of the Linnean Society," by Thomas Horsfield, M. D. 

 F.L.S., &c. and N. A. Vigors, Esq. M.A. F.L.S. was read by 

 Mr. W. S. MacLeay. 



GEOLOGICAL SOCIETY. 



January 21, 1825. — A paper was concluded, entitled, On a 

 recent formation of fresh-water Rock Marl in Scotland, with re- 

 marks on Shell Marl and on the Analogy between the ancient and 

 moder7i fresh-water formations, by Charles Lyell, Esq. Sec. G.S. 



The rock marl described in this communication is an extremely 

 compact limestone, in part of a crystalline structure, and traversed 

 by numerous irregular tubes or cavities. 



As a principal part of its geological interest is derived from its 

 recent origin, the author has drawn a brief sketch of the physical 

 structure of the county of Forfar, in order to explain distinctly its 

 position. 



Those strata are also enumerated in which limestone is found, 

 and its remarkable scarcity in Forfarshire pointed out. 



The districts to which shell marl is confined are next considered, 

 and it appears that deposits of this nature are accumulated only 

 in lakes in two formations ; viz. the inferior or transition sand- 

 stone, and the old red sandstone. 



The Bakie Loch, in which the rock marl occurs, lies in a hollow 

 in sand and gravel. This gravel consists of the broken and rounded 

 masses of the primitive rocks of the Grampians, which are heaped 

 in large quantities upon the old red sandstone in the valley of 

 Strathmore. 



The succession of the deposits of sand, shell marl, and rock 

 marl, in the lake of the Bakie now drained, is then described. 

 The shells and plants enclosed in tlie rock are the same as those 



