374 Philosophical Society of London. 



well characterized grauwacke and grauwacke slate, with 

 equiHy w.ell characterized beds of clay slate and chlorite 

 slate. 



The structure of the rocks hounding the vale of Aberfayle 

 is next described. On tracing this country up to Ben 

 Ledi, alternations of grauwacke and grauwacke slate with 

 clay slate first occur: then comes a fine roofing slate ap- 

 proaching in parts to mica slate, but distinguished by a 

 true grauwacke structure, that is, of grains united by a 

 slaty cement ; only in this case the cement is not clay slate, 

 but mica slate : beyond this the, true mica slate makes its 

 appearance. 



The general deduction from these facts is, that those 

 rocks which have been ranked as primitive schist alternate 

 with rocks of recomposed materials, which belong to the 

 transition class of Werner : but this alternation throws 

 great doubt on the realilv of transition rocks, as distin- 

 guished from primitive, and rather tends to bring back the 

 original divisi(jn of rocks into primitive and secondary. 



PHILOSOPHtCAL SOCIETY OF LONDON. 



The attention of the Society has lately been directed to 

 two Lectures on Pneumatic Chemistry delivered by the 

 Registrar, Mr. Miers. 



After some prefatory observations intended as an intro- 

 duction to the studv of the science, he proceeded to give 

 an abstract of the various theories of chemical affinity, 

 conimeming particularly on the beautiful s\stem of relative 

 proportions of Mr. Dalton, and the grand vet simple doc- 

 trine of electrical energies of Sir H. Davy, — doctrines 

 ■which lead us fairly to indulge in the hope of our being on 

 ihc eve of an important jjcriod, when chemical laws shall 

 be submitted to calculation, and the v\hole science chict- 

 dattJ tiy mathematical principks. Al' kinds of matter ex- 

 isting in tiic universe that arc cognizable to our senses, and 

 that may be denominated elementary, of which there are 

 forty-six, he divided into two classes — Combustible, and 

 Supporters of Combnstion. The individuals of the latter 

 class, comprising only oxygen and chlorine, are distin- 

 guished piincipally by rangmg themselves round the posi- 

 tive pole in the Voltaic circuit ; the former class compre- 

 hendincrall the remaining forty- four undecom pounded bodies, 

 which are distinguished as ranging themselves round the 

 negative pole in the Voltaic circuit, and as oppo.sing them- 

 selves in the relations of affinity to the bodies of the other 

 class. He then entered on the consideration of the known 



properties 



