STATE GEOLOGIST. 59- 



group in this State. They consist of i turrited gasteropod 

 (Laxonana Boydiit) and an obscure Qyathopbylloid ooraL 



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

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

 ous points in the bed of Otter ('rock, in the eastern pan of the 

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

 south of Monro penetrated the same formation and re- 



vealed marked and satisfactory characters. 



Jung the above observations, I have been informed 

 of the discovery of gypsum at Sylvania, in Ohio, just beyond 

 the Stat' 1 line, and am led to regard this as confirmatory evi- 

 of the distinct existence of this group in the southeastern 

 ;<>ur State. It might not be {oo 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 ifl 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 

 a beatiful stone for building purposes. In our own State 

 it has bora already shown to contain gypsum in workable 

 quantities on the shores of the Upper Peninsula, near Little 

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

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

 favorable for exploration are those already 

 mentioned, viz.: the deepest excavations at Montgon 

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

 rges of Otter Creek. 

 tions likewise exist, of the Baliierous character 

 of this formation, in Michigan. Occasional salt springs occur 

 ::. V ... i county, far beyond the outcrop of the baliferous i ' 

 the cuter of the State. The most noteworthy of 

 !s 4] miles south of tin- Paisinville quarries, in the 

 township of Ida. An Artesian well sunk at Detroit in 1S-J9-30, 

 after through 130 feet of unsolidified materials, and 



120 fe< mpact limestone, L! feet of gypsum con- 



taining salt. On the i de of the State, according to 



