THINOLITE NOT A PSEUDOMORPH AFTER GAYLUSSITE. 215 



ative answer to the question as to the nature of the original mineral. It 

 was not gaylussite, nor gypsum, nor anhydrite, nor celestite, nor glauberite, 

 nor, in fact, any one of the minerals which might suggest itself as a solu- 

 tion of the problem. The crystalline form is totally irreconcilable with 

 any of these. This is so clear, from what has gone before, that the question 

 admits of no argument at all. But more can be said: the original mineral 

 was one which does not appear thus far to have been observed in its 

 natural condition, although, as will be shown later, it probably has oc- 

 curred abundantly at numerous other localities. Furthermore, a review 

 of all the artificial salts of calcium, sodium, and magnesium lias failed to 

 bring to light any one which would satisfy the conditions required. 



"It seems, therefore, that any explanation of the original condition of 

 the thiuolite beds of Lake Lahontan must at present rest on hypothetical 

 grounds, and much as a definite solution of the problem is to be desired, it 

 is not now attainable. A few suggestions may not be out of place here, 



The open skeleton forms, consisting now of crystallized calcium 



carbonate, make it seem very probable that the original mineral was a 

 double salt, and that a salt containing calcium carbonate as one of its 

 members. Only on such a supposition is it easy to understand the removal 

 of so large a part of the original material and the leaving behind of these 

 plates of calcium carbonate, marking the original crystalline structure. 

 Whether the original crystals were or were not solid throughout, at the 

 time of their formation, it is not possible to say now with certainty; very 

 probably they varied much at different points in this respect. From the 

 analogy of soluble salt deposited rapidly from aqueous solutions, it seems 

 likely that open, cavernous forms were common, perhaps the rule. But 

 even supposing this to be true, no one can inspect such groups of skeleton 

 crystals as those from the Marble Buttes without seeing that what now 

 remains is only a part of what originally crystallized out of the saline 

 waters of Lake Lahontan. This fact, coupled with the other just men- 

 tioned, that the remaining skeleton consists of crystallized calcite in gran- 

 ular form, gives, a very important hint as to the changes which these 

 crystalline beds have undergone. The successive steps may have been as 



