\ 



401 



and limestones, being composed of lighter sediment, would bo carried 

 farther, and becomo members of the coal measures situated in Liddos- 

 dale, Northumberland, and Berwickshire. 



The formation of the whinstone dykes, one of which was described 

 as running in a NW. direction, for about twenty-four miles, was 

 ascribed by the author to the irruption of igneous matter into fissures 

 previously formed in the earth's crust. 



The beds of gravel and sand, as well as the boulders, the author 

 thought might all be explained on the supposition, that the district 

 had been covered by the waters of the ocean, when they were depo- 

 sited. He adduced facts and arguments for the purpose of shewing 

 that certainly none of these deposits could have been formed by orla- 

 cial action, and that probably submarine currents, or great waves, such 

 as are known to have been produced by submarine eruptions, would 

 be sufficient to account for all the phenomena. 



3. On the Property of Transmitting Light, possessed by 

 Charcoal and Plumbago, in fine plates and particles. By 

 John Davy, M.D., &c. 



The charcoal of the pith of the elder consists of plates of extra- 

 ordinary thinness. It was in examining this charcoal, that the 

 author first observed the property which is the subject of his paper. 

 He detected it by means of the microscope, using a high mao-nifyino- 

 power. By analogy, he ]yfas led to infer that the power of transmit- 

 ting light must belong to charcoal in general, in all its varieties, when 

 reduced to the state of fine powder or filaments, — an influence which 

 he found confirmed by experiment in a number of different instances, 

 as the charcoal of the pith of the sycamore, of the pith of the rush, 

 the fibre of cotton, flax, &c. He also found it to belong to lamp- 

 black, to cork in very fine powder, to anthracite, and plumbago. 



The light transmitted he found to vary in its hues, from almost 

 white, as in the instance of tho thinnest plates of the charcoal of the 

 pith of tho elder, to brown and red of various shades, in the instances 

 of lamp-black, anthracite, and plumbago. 



He considers the property of translucency belonging to charcoal 

 and plumbago, in their finely divided state, as favourable to the 

 opinion now commonly received, that these substances and diamond 

 owe their marked peculiarities not to difference of chemical mixture, 

 but of .mechanical structure. Incidentally, he notices the specific 

 gravities of these substances, — stating, as the result of his own ex- 

 periments, that the specific gravity of charcoal, cork, and anthracite, 

 is about 1.5 ; and that of plumbago about the same, makinnr allow- 



