Heaclden — Broion Artesian Waters of Costilla Co., Colo. 309 



to well up in the middle of the lake, accompanied by a 

 gurgling sound. It is easy to conceive of such a connection, 

 especially if the springs in the eastern and southern parts of 

 the valley owe their origin to the artesian pressure in the basin 

 rather than to individual local causes. This view, on the other 

 hand, has but little plausibility when applied to the Head 

 lake, a small adjacent lake, for this lake becomes almost 

 entirely dry at times. These lakes fill up in the spring time, 

 occasionally receiving water from the Saguache river and the 

 San Luis creek, though this is of very rare occurrence, and 

 have no visible outlet. I do not know the rate of evaporation 

 from a quiet surface at this place, but it must be high, 

 because the sunshine is almost continuous and the temperature 

 in the summer season is high, and high winds are of frequent 

 occurrence. 



I have observed differences of level in the waters of the San 

 Luis lake, varying to possibly 10 feet. The cause of this is not 

 entirely clear ; it seems too great a difference to attribute to 

 surface evaporation. If the water of this lake is supplied from 

 an underground source, it probably owes its origin to more 

 immediate surface drainage, rather than to artesian pressure. 

 This inference is drawn from the character of the mineral 

 matter held in solution rather than from knowledge of strati- 

 graphical relations. The analysis of this lake water gives the 

 following characteristics : First, it is comparatively rich in 

 mineral matter, 54*2 grains of fixed residue in each imperial 

 gallon. Second, it is exceptionally rich in potash salts, 

 potassium carbonate constituting one-fifth of the total, while the 

 corresponding soda salt constitutes one-fourth. Third, the 

 determination of saline and albuminoidal ammonia present 

 exceptional difficulties. 



While the amount of the total solids, 54'2 grains per 

 imperial gallon, seems high, a little consideration of the condi- 

 tions removes this impression. This lake has no visible outlet; 

 it is not known how long it has already existed here, and the 

 accumulation of salts, due to the concentration of pure moun- 

 tain or snow water, might account for all of the salts that we 

 find. Prof. L. G. Carpenter informs me that the evaporation 

 from the surface of this lake may reasonably be estimated at 

 sixty inches per annum, at which rate the water contained in 

 the lake at any one time would be wholly evaporated in about 

 three- years. This is allowing an average depth of about 15 

 feet, a much greater depth than the lake possesses. Such con- 

 siderations lead to the conclusion that the mineral matter held 

 in solution is not sufficiently large to preclude their having 

 been wholly derived from surface waters. . The presence of so 

 large a percentage of potash salts is more consistent with a 



