OF ARTS AND SCIENCES. 240 



by Haidinger) they are often hollow, while the octahedrons are smooth. 

 Cleaveland describes the crystals in general as small and imperfect, 

 and Nichol, in his late work, in like manner, observes, ' They are 

 small, and very small.' It is more than probable that we may yet be 

 able to say of our California gold crystals, they are large, and very 

 large, as much for the benefit of mineralogists, as for a reward to the 

 industry and hard toil of the diggers. 



" The first three of the following figures give a pretty correct idea 



of the size and appearance of the specimens above referred to. The 

 fourth is a group of rare modified forms or hemitrope combinations, 

 such as have occasionally been brought from Brazil and Siberia. There 

 is an example somewhat similar to it in the School of Mines (Paris), 

 and described by M. Dufrenoy in his late treatise on Mineralogy. The 

 crystals exhibited have been very fully described in the American Jour- 

 nal of Science, Vol. X., 1850. 



Two additional crystals recently received present still more remark- 

 able modifications, one of them being a hemitrope. Some descrip- 

 tion of these will be given at another meeting of the Academy." 



Dr. C. T. Jackson added some remarks on the beautiful 

 crystals of native gold from California, exhibited by Mr. 

 Alger, and stated that crystals of this magnitude were un- 

 known in the public collections of Europe, where those of 

 one eighth of an inch in diameter were regarded as very 

 rare and valuable specimens. He also observed, that the 

 octahedral crystals belonging to Mr. Alger appeared like what 

 are called dissected crystals, the centres of the triangular 

 planes of the octahedron being depressed, while the edges 

 were presented in bold relief, and a series of striae, parallel to 

 the edges of the planes, indicated a remarkable decrement 



VOL. II. 32 



