ART, 15. MINERALOGY OF GOUGE CLAYS—SHANNON. Fa 
water which is released upon heating to 110° C., and which is quickly 
regained upon exposure to the air. The mode of combination of this 
water is at present not understood. That it is not inherent to the 
physical structure is proven by the fact that other specimens of 
identical structure, form and size of grain are practically devoid of 
low temperature water. Careful determination, by proper apparatus, 
of the dehydration curves of these materials may give some informa- 
tion bearing on this problem. At present the geologist, dealing with 
ore deposits can not be criticized for failing to distinguish between 
sericite and leverrierite and he is justified, where opportuuity for 
detailed mineralogic work is lacking, in treating all such materials 
simply as sericite. 
The fusibility test is unreliable as all three of the above-described 
clays are fusible before the blowpipe. 
