RESULTS OF ANALYSES. 265 
hydrate solution and subsequently weighed. It was found that 93.60 
per cent of the rock had gone into solution. 
It is evident that a rock so easily attacked by the strong reagents of 
the laboratory will, in the course of time, yield much material to the 
continued action of the weaker natural solvents, although of course some 
of the constituents easily dissolved by hydrocloric acid are nearly insol- 
uble in natural reagents. 
The fresh rock, under similar treatment, yields 93.45 per cent in solu- 
tion. The close agreement of the figures in the two cases is a coincidence 
apparently of no particular significance, but it is peculiar that a rock of 
this character, after losing 27 per cent in solution, is still as readily at- 
tacked by solvents as before. According to the figures, indeed the weath- 
ered rock is slightly the more soluble; but this is probably due to the fact 
that the mica of the fresh rock is difficult to reduce to such a degree of 
fineness as to expose it thoroughly to the attack of the solvents. 
Columns VI and VII show, respectively, the percentage saved and lost 
of each constituent, calculated again on the basis of titanic oxide and 
alumina remaining constant. Silica, which on account of its abundance 
gives a large figure for loss in the total rock, is seen to have yielded but 
27 per cent of its original amount. The very slight loss of iron oxide is 
again made apparent, while, as would be expected, magnesia and lime 
have been removed in relatively large quantity. The excessive loss of 
magnesia as compared with lime is contrary to the general rule, but by 
no means remarkable, as Merrill* cites a much more extreme case in 
a basalt from Crouzet, France, where magnesia has lost 96.38 per cent 
and lime only 47.24 ; while ina diorite from Albemarle county, Virginia, 
the loss is almost the same for both constituents. 
By far the greatest loss has occurred in the alkalies, over 90 per cent 
of the potash having disappeared, while the soda has yielded not a great 
deal less. A considerable loss of the alkalies is the rule in weathering 
involving much chemical change, sometimes one, sometimes the other, 
being removed in larger proportion. 
There is, then, presented in the case under consideration an example 
of weathering which has accomplished the thorough disintegration of 
the rock, with a loss of more than one-quarter of its original constituents, 
accompanied by oxidation and extensive hydration; but in spite of the 
ereat change in the nature of the rock. the composition of the residue is 
such as to indicate that the operation is far from complete. 
* Bull. Geol. Soe. Am., vol. vii, p. 22, and Rocks, rock-weathering, and soils, p. 223. 
+ Rocks, rock-weathering, and soils, p. 225. 
XL—Buty. Grou. Soc. Am., Vou. 9, 1897 
