S9t) Proceedings of Philosophical Societies. [May, 



and iodine described by Gay-Lussac was a compound of oxiode and 

 sulphuric acid, and contained likewise some barytes. 



LINN-EAN SOCIETY. 



On Tuesday, the 4th of April, a paper by Dr. Leach was read 

 on the classification of the insects called notonectides. 



On Tuesday, the 18th of April, a paper by tlie Rev. P. Keith 

 was read, on the ascent of the sap in trees. Mr. Keith took a view 

 of the different hypotheses hitherto proposed to account for the 

 ascent of the sap, and showed that they were all inadequate to 

 explain tlie phenomena. One of the latest of these hypotheses is 

 that of Mr. Knight, who conceives that the ascent of the sap may 

 he owing to what is called the silver grain of the wood. To refute 

 this hypothesis, it is only necessary to mention that some of the 

 tallest plants known have no silver grain whatever. Yet it is obvious 

 that the sap ascends in them as well as in other plants. Mr. Keith 

 considers the hypothesis of Saussure, that the sap is forced up by 

 the contraction of the vessels, as with certain modifications, most 

 likely to be true. 



GEOLOGICAL SOCIETY. 



March 17, 1815. — A communication was read from the Wood- 

 wardian Professor ; the object of which paper is to describe a re- 

 markable variety of geode, several individuals of which were lately 

 met in digging a well at Oakhampton, Devonshire. They occurred 

 in a bed of clay about ten feet deep. Their figure is nearly that of 

 a compressed spheroid, and each ball consists of a nucleus of 

 ochreous oxide of iron enclosed within a shell of a cavernous struc- 

 ture, the shells of which are externally so regular that the mass 

 might easily be mistaken for a fossil madrepore. 



With regard to the mode in which this and similar bodies have 

 been formed, the Professor suggests that the deposition of the beds 

 in which they are formed might have been attended with effer- 

 vescence, and that this spheroidal figure and cavernous structure 

 might have been occasioned by gas uniformly distending, and at 

 length escaping insensibly through the cellular crust by which it had 

 been confined. 



The reading of Mr. Horner's paper on the south-western part of 

 Somersetshire was continued. 



April /. — A short notice from INIr. Horner on the locality of some 

 specimens from the island of Tino, presented by him to the Societj', 

 was read ; also a communication from the Woodwardian Professor, 

 supplementary to his former, on the Cambridgeshire strata. 



This paper furnishes a new locality of the flattened Headington 

 oyster, it having been lately found forming a strong bed at Willham, 

 about six miles north of Ely, in the Fen level, a position whicli 

 ascertains its geological situation to be below tlie chalk. Another 

 remarkable appearance is stated to oocur at Keche, not far from 



