103 



little silicate of copper. One of the purest specimens contained 

 only 1.2 per cent, of impurities, mostly silica, with traces of 

 lime and iron. 



As the oxide of copper of this remarkable vein has not been 

 mineralogically described, the following description is added. 



Substance tesseral, crystallized in cubes, with their solid angles 

 occasionally replaced ; generally, however, massive, with crys- 

 talline structure, sometimes earthy ; no traces of cleavage ; 

 H.= 3 ; S. G.= 6.25 ; color, steel-gray to black ; lustre, metallic, 

 the earthy varieties acquire a metallic lustre on being scratched 

 or cut with a knife ; opaque ; chemical composition, Cu, almost 

 pure ; containing 



Copper 79.86 



Oxygen 20.13 



Mr. E. C. Cabot stated that since the last meeting he had 

 made some experiments to ascertain, if possible, the cause 

 of the non-intermingling of salt water with fresh, in dune 

 sand. 



Having nearly filled a vessel with salt water, he immersed in 

 it a large sponge saturated with fresh water, containing imbedded 

 in it, perpendicular tin tubes, with perforated sides. The exter- 

 nal pressure caused water to appear in these tubes, and to 

 rise to the level of the surrounding fluid. After standing 

 some hours, the water in these tubes was found to be fresh. On 

 reversing the experiment, placing the sponge full of fresh water 

 first in the vessel, and gradually filling the surrounding space 

 with salt water, the same result followed. Capillary attraction 

 seemed to be the force which kept the difl^erent fluids apart. 

 With regard to the difference between fresh water in dune sand 

 and springs, Mr. Cabot said he did not consider it an essential 

 one. In the former case, the water formed, so to speak, a homo- 

 geneous spring; in the latter, underlying strata, and lateral 

 boundaries limited it, and gave it the character of a current. 



In connection with this subject, Mr. Ayres said that since 

 the last meeting, he had read, in Capt. Henry's account of 

 Mexico, some interesting facts. It was there stated that at 

 Corpus Christi, fresh water could be procured within a few 



