228 Geological Society: — 



fresh silver was deposited on these branches, and the fresh copper 

 taken up from the plate, there was not merely a transference of the 

 nitric element from one combination to another, but an actual mole - 

 cular movement of it towards the copper plate, producing an accu- 

 mulation of nitrate of copper there, and a corresponding loss of salt 

 in the liquid that was drawn within the influence of the branching 

 crystals. Hence the opposite currents. 



The amount of action in a circuit of two metals and a saline so- 

 lution must have as one of its regulating conditions the conducting- 

 power of that solution. It appeared by experiment that a strong 

 solution of nitrate of silver offers less resistance than a weak one ; 

 and it was also found, on adding nitrate of potassium to the nitrate 

 of silver, that its power of attacking the copper plate was increased, 

 that the augmentation of the foreign salt increased the action still 

 farther, and that the 2 : 3 law holds good between two solutions in 

 which both the silver and potassium salt are doubled, though it does 

 not hold good if the quantity of foreign salt be kept constant. Si- 

 milar results were obtained with mixed nitrates of silver and copper. 



While these later experiments offer an explanation of the fact 

 that a solution of double the strength produces more than double 

 the chemical action, they do not explain why it should produce exactly 

 three times the effect, or why the ratio should be the same in all 

 substitutions of this nature hitherto tried. The simplicity and wide 

 range of the 2 : 3 law seem to indicate that it is a very primary one 

 in chemical dynamics. 



GEOLOGICAL SOCIETY. 



[Continued from p. 156.] 



March 8, 1871.— Joseph Prestwich, Esq., F.E.S., President, 



in the Chair. 



The following communication was read :— 



" On the Eed Eocks of England of older date than the Trias." By 

 Prof. A. C. Eamsay, LL.D., F.E.S., Y.P.G.S. 



The author stated that the red colour of the Triassic beds is due to 

 peroxide of iron, which incrusts the sedimentary grains as a thin 

 pellicle. This could not have been deposited in an open sea, but 

 rather in an inland salt lake or lakes. The peroxide of iron, which 

 stains the Permian, Old Eed Sandstone and Cambrian rocks, is be- 

 lieved by the author to have been deposited in the same manner, in 

 inland waters, salt or fresh. 



Agreeing with Mr. Godwin- Austen, the Old Eed Sandstone was 

 of Lacustrine origin. The absence of marine shells helps to this con- 

 clusion. The fish do not contradict it ; for some of their nearest 

 living congeners live in African and American rivers. 



The life of the Upper Silurian deposits of Wales and the adjoining 

 districts continued in full force up to the passage-beds which mark 

 the change from Silurian to Old Eed Sandstone. In these transition 

 strata, genera, species, and individuals are often few, and dwarfed 

 in form. Near Ludlow and May Hill the uppermost Silurian strata 

 contain seeds and fragments of land-plants, indicating the neighbour- 

 hood of land, and the poverty of numbers and the small size of the 



