'*>**** 



PROCEEDINGS 



CAMBRIDGE PHILOSOPHICAL SOCIETY. 



November 13, 1854. 



A paper, by R. L. Ellis, Esq., was read, entitled " Remarks on the 

 Fundamental Principle of the Theory of Probabilities." 



Also, " On the Purbeck Strata of Dorsetshire." By the Rev. O. 

 Fisher. 



The object of this paper was to describe the beds from which a 

 series of insect remains and other fossils had been collected by the 

 author, and presented to the Woodwardian Museum. 



The connexion of the Purbeck beds with the Oolitic rather than 

 with the Wealden series was maintained, while both were shown to 

 be unconformable in this district to the cretaceous system. Reasons 

 were given for thinking that the materials, of which both the Wealden 

 and Purbeck were composed, had travelled from west to east ; and 

 the beds of the New Red Sandstone, as they occur in Devonshire, 

 were pointed out as affording a mass of strata which would furnish 

 a detritus of the character of a large portion of the Hastings sands 

 of Hampshire and Dorsetshire. 



In describing the Purbeck beds.the author followed the system of the 

 late Professor E. Forbes, dividing them into upper, middle, and lower; 

 and entered into some detail of the alternations of salt and freshwater 

 conditions that prevailed during their deposition. The aspects under 

 which the same beds appear at different points of the district under 

 examination were particularized, and it was attempted to be shown 

 that these were in conformity with the theory of a current setting 

 from the west towards the east. The mode of occurrence of the 

 remains of insects in the middle and lower Purbecks was somewhat 

 minutely described, and it was suggested that some interesting 

 chronological speculations might be grounded upon it. 



The paper concluded with an attempt to explain the singular frac- 

 tured condition of about thirty feet of the lower Purbeck strata 

 throughout the eastern part of the county. It was supposed that 

 this might have been caused by the deposition of sediment upon the 

 remains of the Portland forest before the mass of the trees had been 

 removed by decomposition ; the sediment, after it had become con- 

 solidated, settling unequally as the carbonaceous matter was gra- 

 dually removed. 



No. XI. — Proceedings or the Cambridge Phil. Soc. 



