124 ECONOMICAL MINERALOGY". 



Carbonates of lime and magnesia, 89.00 



Silica and alumina coloured by oxide of iron, .. 11. 00 



'- With minute proportions of the chlorides of sodium and calcium. 



They therefore all belong to the class of marly clays, which are so constantly associated with 

 fossil salt. 



Having noticed the striking similarity in the formations near the Onondaga springs to those 

 of many localities of fossil salt, I must also advert to a fact which by many persons is thought 

 greatly to favour the theory now under consideration. It is, that the strength of the brine is 

 influenced by the height of water in the Onondaga lake. Thus it is asserted, that in the 

 early part of the summer, when the water in the lake is high, the brine contains a much 'larger 

 amount of saline matter than at any other time. Dr. Wright, the late superintendent of the 

 salt-works, informed me, that during the spring of 1836, when the water in the lake attained 

 an unusual height, the brine at the Salina well had a density of 79° by an instruinent on which 

 the point of saturation was 100°; whereas ordinarily it does not exceed 63° or 64°. This 

 extraordinary density continued only a short time ; but a density of 70° is said to be no "un- 

 usual occurrence under such circumstances. The increased strength of the brine in the early 

 part of the season is supposed to be accounted for by the fact, that as the quantity of water 

 discharged from the pumps during the winter is comparatively small, the brine continues for 

 a longer time in contact with the fossil salt, and becomes more strongly impregnated with it ; 

 and again, when the quantity of water in the lake is large, the increased pressure upon the 

 river of brine below, causes the stronger solution to rise higher in the well than at other times. 

 We have here a singular illustration of the manner in which the same general fact is em- 

 ployed to strengthen theories directly opposite. Dr. S. P. Hildreth, in a paper on the bitu- 

 minous coal deposits in the valley of the Ohio, etc., thinks the opinion that the brine springs 

 in the valley of the Ohio are not supplied from a deposit of rock salt, but from salt in small 

 grains or particles pretty equally diffused, strongly confirmed by the fact that the brine be- 

 comes weaker in a well worked very constantly, and the necessity of boring deeper to renew 

 the strength of the water. For, says he, " if the water was supplied from a deposit of pure 

 •solid salt, the well would remain of uniform strength. Another proof is founded in the fact, 

 that the deeper wells are supplied with a stronger water ; showing that the further the sahne 

 strata are .penetrated, the more certain they are to yield a strong brine."* 



•The fact just stated, viz. that the strength of the brine increases with the depth of the well, 

 applies also to the Onondaga springs ; and I should have offered it, among others, in favour 

 of the theory that they have their origin in fossil salt ; for, if X am not mistaken, at every lo- 

 cality of this mineral, the brine increases in strength from the surface, until it is in immediate 

 contact with the bed from which it derives its saline impregnation. Nor does there seem to 

 me to be any thing in the fact that the strength of these brines diminishes on being worked, 

 which is at all inconsistent with this view. 



* American Journal of Sdence^ XXIX. I. 



