GEOLOGY. 



297 



smallest one, which is the most perfect, is so entirely free from any 

 adhering portion of the matrix to which it must have been attached, as 

 to lead to the belief that this matrix was a much softer material than 

 the quartz in connection with which the gold is usually found. The 

 exact locality of this crystal is not known. ]t presents four pretty reg- 

 ular faces, and has three of its solid angles perfectly formed to a point. 

 One of the faces is depressed by a very deep cavity, which extends not 

 quite to the edges of the plane, but so near them as to leave a narrow 

 ridge, or border, all around the cavity and parallel with the edges, thus 

 giving the same triangular outline to each. It appears as if the crys- 

 tal had been in a liquid state, and that soon after the outside had con- 

 gealed, the inner portion, or a part of it, had run out, leaving the sur- 

 rounding consolidated edge referred to. Something similar to this 

 takes place in the formation of artificial crystals. Some of the crystals 

 of gold in possession of Mr. Alger are macles, and present rare and 

 curious forms. The accompanying figure repre- 

 sents one of the most remarkable of these forms. 

 The great size of the crystals, and the fact that 

 some of the cavities contained portions of oxide 

 of iron, probably produced by the decomposition 

 of pyrites, have led some to regard them as 

 pseudomorphs of sulphuret of iron. ' ' I am not 

 disposed," says Mr. Alger, " to ascribe any 

 such forced and unnatural origin to these beau- 

 tiful productions. I believe them to have been 

 formed under the ordinary circumstances of 

 crystallization, either in an open space or while 

 surrounded by a matrix so soft and accommodating, as to allow them 

 full freedom to take the form it was intended they should take." 



Mr. Teschemacher, at the Boston Natural History Society, April, 

 observed that some of the octohedrons of gold in possession of Mr. Al- 

 ger measured five sixteenths of an inch at the base of the pyramid. 

 He had never seen crystals from other localities exceeding one six- 

 teenth of an inch, and thought that this circumstance was an indication 

 that the gold deposits in California were far larger than any hitherto 

 explored. 



The largest of the crystals referred to were obtained from a very 

 choice and beautiful collection of specimens, made with great care, and 

 no small expense, by Mr. Platt of New York. This gentleman, dur- 

 ing a residence of two years in San Francisco, and while occupying a 

 situation which brought him in contact with persons returning from the 

 mines, has purchased the most interesting specimens obtained by them. 

 He has consequently been rewarded by the finest collection hitherto 

 brought from California. It comprises a great variety of ramified, ar- 

 borescent, dendritic, and other imitative forms, here and there showing 

 crystalline faces, all of them being sometimes most fantastically joined 

 together in the same specimen. In obtaining this collection, Mr. Platt 

 states that he examined gold to the value of more than four millions 

 of dollars. 



