132 Mr. D. Forbes's Researches on the 



Gold from the Head of the Valley of Tipuani.— Still higher up, 

 and in the small streamlets which, when united, form the river 

 of Tipuani, gold-washings are carried on by parties of one or 

 more men, whose success is extremely variable, but who probably 

 make, under ordinary circumstances, at least some two dollars a 

 day, independent of the lucky chance of hitting upon some larger 

 auriferous deposit. The gold in such washings, as might be 

 expected from being nearer its source, is not so pure as lower 

 down, and also does not present that smooth or flattened ap- 

 pearance so characteristic of the gold derived from the washings 

 in the main river, and from which it is at a glance distinguished. 

 It resembles far more the product washed out of gold quartz or 

 veinstone after crushing. In fact it has not been as yet pounded, 

 flattened, and smoothed by the constant action of the pebbles of 

 the river into which it sooner or later might expect to be carried 

 down. 



Even the smallest particles of such gold, when dissolved, gene- 

 rally show quartz or other gangue remaining insoluble; and for 

 this reason, as well as from minute air-cavities which the irre- 

 gularity of form much favour, the specific gravity is generally 

 lower, and in the case of the specimen here reported was found 

 to be 16'07 at 60° F., although small pieces were employed as 

 free from impurity as could be procured. Some of the pieces 

 presented distinct traces of monometric crystallization, the edge 

 of the octahedron being visible on several specimens. 



The analysis was made as in the former case, only with the 

 exception that the amount of insoluble, which when seen under 

 the microscope appeared to be nearly altogether quartz, was deter- 

 mined by dissolving the chloride of silver obtained in the course 

 of analysis in caustic ammonia, and afterwards deducting the in- 

 soluble residue from the previously-found amount of chloride. 

 The following percentage results were obtained : — 



Gold 91-96 



Silver ..... 7'47 



Iron traces 



Insoluble .... 0*57 



100-00 



The various specimens of gold from the valley of Tipuani here 

 examined will consequently give the following results : — 



^alfeyf Romanplaya. QrtSk. AuC ° ta - 



Gold. . . 9196 94-189 93-51 94*73 



Silver . . 7-47 5-811 6-49 5'23 



Iron . . trace .... .... 0*04 



Matrix . . Q-57 



100-00 100-000 100-00 100-00 



