GEOLOGICAL AND NATURAL HISTORY SURVEYS. 215 



is occupied chiefly with an account of work under the direction of 

 Doctor Houghton, and brings together a connected statement of the 

 " Succession of Strata in Michigan as published in 1838-1841." 



The definite exhibit of the geological succession in the Lower Penin- 

 sula of Michigan had never been enunciated before the results of 

 1859-18G1 were attained. 



The Carboniferous limestone lind never before been irtentifie,! iu the State, 

 but had genernlly been confounded with the Monroe and Mackinac limestones. 

 The Michigan salt group was a totally new and previously unsuspected forma- 

 tion. * * * The fact that the formation underlies all the central part of 

 the State was not only unsuspected, but was a fact out of harmony with the 

 theory then prevailing respecting the origin of gypseous deposits. Geologists 

 generally had held gypsum to be a secondary product, resulting from chemical 

 reactions in the rocks, and especially from the action of sulphuric acid on 

 limestones and dolomites. Tlie conception of a continuous gypsum formation 

 having a sedimeutjiry origin, hnd probably seldom if ever been entertained.' 



That view resulted from researches made in Michigan in 1859-GO, 

 and at this day scarcely any other finds defenders. Salt basins, there- 

 fore, are the sites of ancient areas of salt water which have gradually 

 dried up. 



Before these investigations the gypsum of Mackinac and Grand 

 Rapids had been regarded as of one geological age. It was now 

 shown that th.e Mackinac gypsum is of the age of that in central New 

 York and ou Sandusky Bay. It foUov^ed that the whole peninsula is 

 underlaid by a second and deeper salt basin — the Salina formation — 

 and that quite probably this basin would also be found a source of 

 brine supplies. 



The report showed that the salt springs of the Peninsula follow 

 especially the lines of the outcrop of the principal salt basin, and 

 mark the geological boundary of the formation. It showed that the 

 area of the Peninsula had never been subjected to disturbing agen- 

 cies; hence the strata were but little fissured, and few opportunities 

 existed for the ascent of the brine from deep underlying formations. 

 It raised the query how brine, which is heavier than water, should be 

 made to ascend, as had heretofore been assumed possible, several 

 hundred feet through fissures accessible to shallower fresh waters, 

 even if such fissures existed, and showed that, of necessity, the undi- 

 luted brine from any deep-seated formation must be pumped up; 

 ond that if salt water overflovrs at an artesian boring, it results 

 simply from a head of fresh water mingled W'ith some accidental 

 supply of brine. It showed that the marginal salt springs of the 

 State are simply drippings from the salt-bearing formations, prompt- 

 ed by the descent of fresh waters into them, and greatly diluted by 

 rains falling near the locations of the springs. It showed that the 



* Winchell, Sparks from a Geologist's Hammer, pp. 208, 209. 



