DEXDRITrC SINTER. 267 



stances detected in the water (excepting- manganese and bromine) and, in 

 addition, traces of cobalt and lithinm. They also contain some organic 

 matter which evidently consists in part of the pnpa cases of insects. These 

 sinter masses grow to a maximum diameter of about four feet and a height of 

 about three feet. Tlie outlines assumed resemble those of an isolated clump 

 of trees and bushes seen at a distance. They appear to grow laterally as well 

 as vertically, and thus overhang the level, somewhat pebbly ground upon 

 which they stand. Broken masses show a porous, sponge-like structure, but 

 I detected no definite crystal forms. There appeared to be no opportunity 

 to trace out the history of these masses, nor could I detect any definite 

 nucleus. When once a small accretion of this sort has started, it would 

 appear that the spongy mass draws up the brine from the moist ground and 

 affords an opportunity for the evaporation of the fluid. Why the masses 

 consist substantially only of calcium carbonate is not certain; but it seems 

 not improbable that when first formed they contain a consideral)le excess of 

 tliis rather insoluble compound, which separates out in a comparatively pure 

 form, as is usual in cases of slow crystallization from mixed solutions, and 

 that they are further purified by the winter rains. Though the inception 

 of these masses has not been traced, it is easy to imagine how it might 

 occur. Any small lump of pumice, fragment of wood, or other porous sub- 

 stance partially immersed or lying upon the wet mud near the edge of the 

 lake would tend to accumulate a crust of salts upon its upper surface through 

 capillary attraction and evaporation, and the spongy accumulation would 

 then continue to absorb the fluid. These sinter masses appear to answer to 

 some of the tufas associated with the thinolite studied by Messrs. King, 

 Russell, and E. S. Dana. They are certainly still forming and are all of 

 recent origin. If any substitution has taken place .in these sinters it must 

 have fidlowed almost immediately upon deposition and probably accom- 

 panied dehydration. However this may be, it is an interesting and some- 

 what important fact that sinters composed substantially of calcium carbon- 

 ate can grow directly from a fluid containing large quantities of sodium 

 carbonates and borax and which holds only small amounts of calcium car- 

 bonate in solution. 



