Abstracts. 



The Solution of Silica under Atmospheric Conditions. By C. \\'illard 

 Hayes. 

 While it is well known that under conditions prevailing at con- 

 siderable distances below the earth's surface silica is one of the more 

 easily soluble substances entering into the composition of the earth's 

 crust, it is commonly regarded as the mineral least liable to be 

 affected by solvents under ordinary atmospheric conditions. Some 

 recent observations, however, show that even quartz pebbles are not 

 proof against chemical as well as mechanical erosion. At several 

 widely separated points in West Virginia and Tennessee occur coarse 

 conglomerates, in two cases Carboniferous and a third Cambrian in 

 age, in which the projecting portions of the pebbles have been deeply 

 etched, evidently by solution. The pebbles vary in size up to an inch 

 in diameter and are composed chiefly of vein quartz and quartzite 

 together with a few of chert and feldspar, embedded in a coarse 

 sandstone matrix. The projecting portions of these pebbles, particu- 

 larly those composed of quartz and quartzite, are deeply pitted with 

 rough, irregular surfaces, in many cases as much as a third of the 

 pebble having been removed. From the form assumed by most of 

 the pebbles, it would seem that their interior was more easily soluble 

 than the outer portions. The latter usually forms a sharp rim within 

 which is a depression with a slight elevation at the center. The 

 etching is not confined to the larger pebbles, for on closely examining 

 the surface of the matrix it is seen that in many places the projecting 

 portions of the Eand grains have been removed, leaving a more or less 

 smooth mosaic. A comparison of these etched pebbles with the glypto- 

 liths or facetted pebbles described by Woodworth and others shows 

 clearly that thev are not produced by the same agency as the latter, 

 namely wind driven sand. Everything, on the other hand, ])oints 

 clearly to solution. 



Again, numerous geodes from the Carboniferous limestone in 

 Tennessee, collected by Campbell and Taff, show etching similar to 



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