Geological Society. 55 



from the moon's western limb. The whole time of the occul- 

 lation was 1'' 7"' 4-4'-5. 



After this, the reading was commenced of a paper by 

 Mr. Henry Atkinson, of Newcastle-upon-Tyne, " On astro- 

 nomical and other refractions ; with a connected inquiry into 

 the law of temperature in different latitudes and altitudes." 

 As the reading of this paper will be resumed at a subsequent 

 meeting, an abstract of the whole may with propriety be de- 

 ferred. 



GEOLOGICAL SOCIETY. 



Jan. 21. — A paper was concluded, entitled " On a recent 

 formation of freshwater rock marl in Scotland, with remarks 

 on shell marl, and on the analogy between the ancient and 

 modern freshwater formations." By Charles Lyell, Esq. Sec. 

 G. S. 



The rock marl described in this communication is an ex- 

 tremely 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 oi"der 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 con- 

 sidered, and it appears that deposits of this nature are accu- 

 mulated only in lakes in two formations ; viz. the inferior or 

 transition sandstone, 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 sand- 

 stone in the valley of Sti"athmore. 



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 inclosed in the rock are the same as 

 those 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 Charce, the latter being fossilized in such a manner as to 

 present a perfect analogy to the gyrognite 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 Forfar- 

 shire, and some which the author has examined near Ilomsey 



in 



