98 ABSTRACTS 



fringe." This system of fractures en echelo>i pervades the entire joint. 

 Specimens were exhibited showing the joint structure above described, 

 and also examples of fracture produced by blasting in a quarry, in 

 which specimens there was a central warped surface corresponding to 

 the joint-plane, and a system of marginal fractures comparable to the 

 joint-fringe. The oblique imbricating plates formed by this fracture 

 suggest a comparison with the "diagonal fissility" of Van Hise. The 

 obliquity in the case of joints is found of value in determining the 

 axis of breaking tension, whatever the nature of the force which pro- 

 duced the joint or fracture. This axis is a normal to the oblique 

 marginal fractures. In mapping joints, a short straight line like the 

 "strike" line crossed by short oblique lines having the obliquity of the 

 observed marginal fractures of the fringe was proposed as a symbol. 

 (Not to be published in the Bulletin of the Geological Society.) 



Notes on Rock Weathering. By George P. Merrill. 



This paper was in direct line with those read at previous meetings 

 of the Society, and had to do with the ultimate products of decompo- 

 sition as shown in the transition of a fresh micaceous gneiss to the 

 condition of a bright red residual soil. The results of physical and 

 chemical analyses were presented, and on the assumption that the alu- 

 mina had remained essentially constant during, the decomposition, it 

 was shown that 44.67 per cent, of original matter had been lost through 

 the solvent and leaching action of water. The writer stated that on 

 the basis that such results were rather under than above the actual 

 amounts he had from a large number of analyses been led to the con- 

 clusion that an ordinary crystalline siliceous rock of a granitic or 

 gneissoid type in passing by decay from its fresh condition to that of 

 soil might lose about 50 per cent, of its original constituents. 



The cause of the red color of the residuary material was discussed. 

 The writer agreed with Professor Crosby in that the color was wholly 

 superficial, but thought that such color might be due not wholly to dehy- 

 dration of the ferric oxides present, but also to the presence of a large 

 amount of coloring matter, the iron oxides having been shown to be 

 largely insoluble, and hence accumulating in the residue along with 

 the alumina. The subject of zeolites in soils, and their efficacy as con- 

 servators of potash was discussed, the conclusions being that not only 

 is there no proof of the formation of zeolites, during the ordinary proc- 

 esses of true weathering, but also that even did zeolites exist in the 



