16 GEOLOGY OF OHIO. 



distinct types of limestone rock. A considerable part of it is very tough, 

 strong, dark blue limestone, while other portions are white, porous and 

 soft. 



This formation has a great extension throughout the peninsula and 

 the islands of northern Michigan. It constitutes the greater mass of 

 the island of Mackinac and is also found carrying beds of gypsum and 

 possibly salt in the mainland of St. Ignace and northward. In Macki- 

 nac Island the concretionary, conglomeritic and brecciated phases are 

 very strikingly shown. It no doubt underlies all the lower peninsula. 



The line of junction between the Niagara and Waterlime is some- 

 times obscure and no means are at hand for drawing sharp lines of divi- 

 sion. 



All that has been thus far said applies mainly to the formation as 

 found in outcrop ; but well-reamings brought up from considerable 

 depths at various points in the state render it certain that the principal 

 features now given mark the formation below ground as well as above. 

 There is no reason to doubt that the Waterlime has as wide a distribution 

 in the subterranean geology of Ohio as the formations alread} r described. 

 It is to be found in every part of the state in which it is due. 



The formation has come into new prominence, through. the revela- 

 tions of the drill, within the last few years. In regard to no other ele- 

 ment of the series have the geologists been so wide of mark as in 

 regard to the Lower Helderberg formation. What belongs to it was 

 taken from it and given to a stratum that has no existence in the state ; 

 and it was credited with but one-sixth of its real thickness. Its out- 

 crops ought to have shown that it has a much greater thickness than 

 was assigned to it, since they cover several scores of miles in an east and 

 west line. A large amount of additional investigation is demanded to 

 put it in order, and to secure such a mastery of it as to be able to 

 determine from an inspection of any outcrop what place it holds in the 

 general series, will be a valuable service to the geology of the state. 

 Winchell established, approximately, one horizon in it which promises 

 to be of some service, namely, the horizon of the Tymochtee Slate, a bed 

 of dark blue slaty limestone that is found in outcrop in the valley of 

 Tymochtee Creek near Care}-, Wyandot county. It is below the middle 

 of the formation and probably within one hundred to two hundred feet 

 of the Niagara limestone. A few other facts can be added that bear upon 

 the same point. The excessively hard and strong dark blue pure lime- 

 stone of Allen, Hardin and Hancock counties and some adjoining 

 regions, which often has its surface conspicuously marked with sun- 

 cracks, belongs to the middle portion of the formation, but probably 

 above, rather than below the middle. 



The purity of the limestone renders- it easily soluble in atmospheric 

 water, and more than any other lime of the state it gives rise to subter- 

 ranean water courses. The most striking example in this line is to be 



