prevailed, to salt with clay in such a large proportion as 

 to make it doubtful whether to call it clay with salt inter- 

 mixed or salt with clay intermixed. This latter deposit 

 forms when seasons of excessive rainfall occur, or, if the 

 clay is purely local in the salt bed, it is formed in that 

 portion of the lake nearest the influx of the streams. I 

 show specimens of both kinds. A section of a thick deposit 

 of rock salt gives a good idea as to the greater or lesser 

 amount of rainfall, and of the comparative lengths of 

 periods of little rain and periods of excessive rain. The 

 marls immediately overlying the salt beds show the rainfall 

 to have been more than would allow the lake to become 

 saturated brine. 



On the rock salt thus formed I propose to trace the 

 action of fresh water brought into contact with it, and to 

 indicate the results following from such contact. I will 

 examine the action of 



(1) Water in a state of rest 



(2) Water descending by gravitation and passing over 

 beds of salt in its course to a lower level. 



(3) Water descending by gravitation to beds of salt 

 beloiv the surface of the earth, and reappearing as brine 

 springs at the surface, but at a higher level than the salt 

 beds. 



(4) Natural water set in motion, or its motion accele- 

 rated, by artificial means, such o.s pumps. 



(5) Water conveyed artificially to deep salt beds, and 

 then pumped wp again. 



Under these heads, which, though apparently similar, are 

 really distinct, it will be possible to class all the phenomena 

 exhibited by the action of water on beds of rock salt. 



I. — Water in a state of rest. 

 Water at times reaches a bed of salt, and can proceed no 

 further, but remains motionless. This is not a very frequent 



