Shell 



Coral 



Geobigerina 



limestone 



rock 



ooze 



0.000039 



0.000201 



0.000137 



0.001843 



0.003014 



0.003091 



CIIEMICAL ACTION OP WATER 173 



The relative solvent power of salt and fresh water has often 

 been discussed, and in some eases actual tests have been made. 

 Thoulet^ obtained the results given below, the tests extending 

 over a period of but 24 hours. Though not conclusive, they seem 

 to show that, so far as the particular materials tested are con- 

 cerned, fresh water is by far the more energetic. The figures 

 give the loss in grams from a cubic centimeter. 



Pumice 



Sea water 0.000105 



Fresh water .... 0.000832 



the sandstone matrix in which the pebbles are embeclded is also pitted, 

 possibly by the same process of solution as that which has affected the 

 pebbles, but such a surface might also be produced by mechanical means in 

 ease the cement were less indurated in some places than in others. 



''The second case is on Clifty Creek, White County, Tennessee. The con- 

 glomerate, also a member of the coal measures, forms the bottom of a small 

 canon, and is covered by the creek at high water, but uncovered throughout 

 the greater part of the year. The matrix is a coarse white sandstone which 

 weathers yellow by the oxidation of the slightly ferruginous cement. Em- 

 bedded in this are rather abundant pebbles, varying in size up to two inches 

 in diameter, and composed chiefly of quartz, with a few of chert and pos- 

 sibly of quartzite. The projecting portions of these pebbles have been in 

 part removed, though they still project somewhat above the enclosing matrix. 

 As in case of the Nuttall conglomerate, the exterior portions of the pebbles 

 are less easily affected than the interiors, and when the pebble has been 

 a third or half removed the outer shell forms a rim within which is a de- 

 pression with a slight elevation in the centre. The chert pebbles show less 

 evidence of corrosion by a solvent than those composed of quartz. Their 

 upper surfaces are somewhat worn down and even slightly hollowed, but 

 this might easily have been produced by mechanical means, which is not 

 the ease with quartz. 



''The third ease is a block of conglomerate from Starrs Mountain, Ten- 

 nessee, collected by Mr. Bailey "Willis. This is of Lower Cambrian age. 

 The matrix is a coarse feklspathic sandstone containing layers of well- 

 rounded pebbles, mostly quartz, with a few probably of some feldspar. The 

 former are between one-half and one inch in diameter and the latter some- 

 what larger. The projecting portions of the quartz pebbles on one side of 

 the block are almost entirely removed, and as in the other eases evidently 

 by solution. A slight rim projects above the matrix in which the pebbles 

 are embedded; within this is a depression, while a slight elevation occupies 

 the centre. 



"The projecting portions of the feklspathic pebbles also are partly re- 

 moved, but this may be due to corrasion instead of corrosion, that is, to the 

 action of mechanical rather than chemical agents. The pebbles on the 

 lower side of the block have their original water-worn surfaces without any 

 trace of etching. ' ' 



^ Comptes Kendus Paris Academic, Yol. 110, 1890, p. 652. 



