264 C. H. SMYTH, JR—WEATHERING OF ALNOITR. 
Of the abundant constituents, silica and magnesia have contributed 
almost equal quantities to the material carried away in solution. The 
iron oxide has yielded only a very small amount, differing but slightly 
from the assumptively insoluble titanic oxide and alumina. In view of 
the evident presence of considerable organic matter in the weathered 
dike, a decided amount of solution of the iron oxide might be looked for ; 
and an irregular distribution of color in the weathered rock, as well as 
the staining of the mica, also points to this conclusion. Although this 
suggests the possibility that the figures for loss are too low, nevertheless 
oxygen has had ready access during the weathering, and oxidation has 
been a prominent feature of the process; so that it seems probable that. 
the iron loss has not been enough greater than indicated by the figures 
to point to any serious error in the method of caleulation—a conclusion 
sustained by the relation between titanic oxide and alumina. It is prob- 
able, as pointed out by Merrill, that in all cases where this method is 
employed the estimate of material lost is too low, rather than too high. 
Of the less abundant constituents, lime has supplied only a moderate 
amount of material to solution, with potash not far behind it. 
The total amount of material removed in solution, about 27 per cent, 
seems small in view of the very decided change in the physical character 
of the rock—a complete disintegration and marked change of color. 
Nevertheless, it is far in excess of the amount removed from some thor- 
oughly disintegrated acid rocks ;* and although in basic rocks physical 
and chemical changes keep closer together, the disintegration, while 
sufficient to destroy the coherence of the rock, has not reduced it to a fine 
clay, and is hardly to be considered excessive as compared with the 
amount of chemical change. 
As to the completeness of the weathering, from the chemical point of 
view it can scarcely be thought that a rock containing 13 per cent of mag- 
nesia and 5 per cent of lime, and made up largely of readily recognizable 
minerals of greater or less complexity of composition, has reached a con- 
dition of stability under surface conditions. The composition is quite 
different from that of a typical residual clay, the ultimate product of 
weathering, and there can be no doubt that the process is far from 
complete. 
The behavior of the weathered rock with solvents is suggestive in this 
connection. A sample was digested in very dilute hydrocloric acid upon 
the water bath for six hours, then for two hours with the acid diluted with 
only an equal volume of water. The residue was treated with sodium 
* Cf. G. P. Merrill, Bull. Geol. Soc. Am., vol. vi, p. 324. 
