92 Outlines of Geology. 



neutralise themselves, and are certainly inadequate as general 

 agents, though their occasional and local efifects may, if not duly 

 weighed and compared, mislead us in the estimate of their powers. 

 Indeed, of accumulation rather than of decay, of growth rather than 

 of wasting away, we have further remarkable illustration in the 

 phaenomena of submarine and subterranean forests of trees mani- 

 festly buried in their natural position, as on the coast of Lincoln- 

 shire, Pembrokeshire, and Lancashire, in the valley of the Thames 

 near Purfleet, and elsewhere. We also have instances of the agglu- 

 tination of sand into sandstone, on the north coast of Cornwall ; of 

 aestuaries filled up by alluvial debris, as in the Cornish stream- 

 works ; and many other attestations of the extension rather than 

 the destruction of habitable surfaces. 



Having now sketched the business of the succeeding lectures, 

 and having briefly enumerated the various theories which it will 

 be my object more fully to discuss and explain, I shall proceed to 

 examine, in detail, the most superficial strata of the globe, and to 

 pursue that plan of geological inquiry of which the heads have 

 been enumerated. 



(To be continued.) 



Art. IX.— 0;i the Hygrometnc Properties of Insoluble and 

 Difficutly-soluble Compounds. By Mr. T. Griffiths. 



[Communicated by the Author.] 



The power of absorbing moisture from the atmosphere has been 

 shewn by Professor Leslie not to be peculiar to acids, alkalies, 

 and deliquescent salts, but to be also possessed by several insoluble 

 chemical compounds. 



His experinients on these are not, however, very numerous, and 

 are all chiefly in reference to the degree of dryness they indicate 

 upon the hygrometer, when submitted to the action of air satu- 

 rated with aqueous vapour. The subject appearing one of con- 



