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60 Scientific Intelligence. 
the same. They have been tested for ten months by Mr. Michel, 
at the physical laboratory of the Sorbonne, and as a result it is 
found that their electro-motive force and resistance do not undergo 
the — change, as long as they are heated to a constant tem- 
era 
Z When heated by a gas burner, they form a very convenient 
source of electricity for the laboratory, only requiring a match to 
ut them in action, while, when constructed on a larger scale and 
heated by a coal-burning furnace, they form an excellent source 
of a powerful and constant current of —— for papas or 
other purposes.— Les Mondes, 231, Oct. 9th, 1 
IL GroLtocy AND NaTuRAL History. 
. Decomposition of Crystalline Rocks ; by T. Srerry Hunt.— 
Dr. T, Sterry Hunt gave some account of the crystalline rocks of 
the Blue Ridge and their decomposed condition, as seen by hi him 
at various points in the region to the southwest of Lynchburg, 
They are principally gneisses with hornblendic and mica- 
ceous schists like those of the Montalban or White Moqniae series, 
and are completely decomposed = - sa of fifty feet or more 
from the surface, being changed i unctuous reddish brick- 
clay, in the mids t of which the Saaebecided layers of quartz are 
seen retaining their + Sigg to — and showing the highly in- 
clined attitude of the strata. In the adit of a mine, where the 
rocks had been penetrated to a considerable distance, the coarsely 
feldspathic gneiss was found completely kaolinized, but free = 
the ferruginous coloring of the surface, while farther i in, after 
ing through a partially decomposed portion, the hard, ‘onchanged 
rocks were met wit similar decomposition of the gneissic and 
granitic rocks in Brazil, extending to a wigs of one hundred feet, 
has been well described by Hartt, and is known in many other 
subterranean drainage and prevent the accumulation of water in 
pools and lakes 
_ nature of these chemical changes of the gneissic and horn- 
blendic rocks was next considered. It consisted essentially in the 
seabuas, in the form of soluble basal f the alkalies, lime 
magnesia of the silicated minerals and the peace of the 
residues. The iron-oxide from these has also been in great part 
auctra out by subsequent processes, and was the source of the 
immense deposits of hydrous iron ores which are found at the foot 
= ce barrier range of the Blue Ridge throughout the Appalachian 
alley. 
The great antiquity of this chemical decomposition of the rocks 
was next alluded to. It was, in his opinion, effected at a time 
when a highly it aiiscaphets and a climate very different 
m our own prevailed. That this decomposition had extended 
to the crystalline rocks to t the northeastward he did hot doubt ; 
and he ascribed the absence of regi 
+ 
