STATE GEOLOGIST. 59 



group in this State. They consist of a turrited gasteropod 

 ( Laxonema Boydiif) and an obscure Oyathophylloid coral. 



The group was again recognized at the head of Ottawa Lake, 

 in the south-western part of the county, and again at numer- 

 ous points in the bed of Otter Creek, in the eastern part of the 

 county. The deepest of the Plumb Oreek quarries, two miles 

 south of Monroe, have penetrated the same formation and re- 

 vealed marked and satisfactory characters. 



Since making the above observations, I have been informed 

 of the discovery of gypsum at Sylvania, in ©hio, just beyond 

 the State line, and am led to regard this as confirmatory evi- 

 dence of the distinct existence of this group in the southeastern 

 part of our State. It might not be too much to allege that the 

 gypsum exported from Sandusky, probably holds a position in 

 the same geological horizon. 



The economical importance of the Onondaga Salt Group of 

 rocks is very great. It is the source of all the salt and gyp- 

 sum of the State of New York, and supplies at Gait, in Canada 

 West, a beatiful stone for building purposes. In our own State 

 it has been already shown to contain gypsum in workable 

 •quantities on the shores of the Upper Peninsula, near Little 

 Pt. au Chene. The occurrence of gypsum at Sandusky and 

 Sylvania, in Ohio, justifies the search for it in Monroe county. 

 The localities most favorable for exploration are those already 

 mentioned, viz.: the deepest excavations at Montgomery's 

 quarry, the Plnmb Creek quarries, those at the head of, Ottawa 

 Lake, and the gorges of Otter Creek. 



Some indications likewise exist, of the saliferous character 

 of this formation, in Michigan. Occasional salt springs occur 

 in Monroe county, far beyond the outcrop of the saliferous sand- 

 stones of the center of the State. The most noteworthy of 

 these is 4J miles south of the Kaisinville quarries, in the 

 township of Ida. An Artesian well sunk at Detroit in 1829-30, 

 after passing through 130 feet of unsolidified materials, and 

 120 feet of compact limestone, passed 2 feet of gypsum con- 

 taining salt. On the opposite side of the State, according to 



