44 EEPOET OF THE 



mountains was once an ocean bed, over which were strewn the 

 various sediments that have formed the groups of rocks, which 

 stretch with more or less regularity from one' end of this area 

 to the other. Geological agencies have left this ocean floor, in 

 an undulating position; and subsequent denudation of the 

 higher points, has worn many holes through the upper layers 

 of rock, where they have oeen pushed up into exposed atti- 

 ■ tudes. The city of Cincinnati stands upon a dome of older 

 strata, which have been uncovered by the planing off of the 

 higher beds. The strata dip in every direction from this vicin- 

 ity. Toward the north, however, the dip is least, and some- 

 thing of a ridge extends towards the common corner of Ohio, 

 Indiana and Michigan. It bifurcates, however, before reaching 

 that point, and the east branch runs up to Monroe county, 

 crosses Lake Erie and subsides in Canada West; while the 

 west branch passes across northern Indiana and Illinois, to the 

 head of Lake Michigan, and thence north-westward. 



A ridge extends through Canada, along a line nearly parallel 

 with the St. Lawrence, to the region north of Lake Ontario, 

 and thence trends north-west around the northern shores of 

 Lakes Huron and Superior. The rocks around the shores of 

 Lake Huron dip south-west and south, away frem this ancient 

 axis ef elevation. 



It appears, therefore, that the Lower Peninsula of Michigan 

 is surrounded on all sides by ancient axes of elevation; and 

 even if the surrounding regions do not in all cases actually 

 occupy a higher level, we must expect to find the strata dip- 

 ping from all sides toward the centre. Each rocky stratum of 

 the Lower Peninsula is, therefore, dish shaped. All together, 

 they form a nest of dishes. The highest strata are near the 

 centre of the peninsula; and passing from this point in any 

 direction, we travel successively over the out-cropping edges 

 of older and older strata. The irregularities in the shape of 

 these dishes, will be pointed out in the sequel. 



The southern part of the Upper Peninsula is covered by the 

 lower members of the southward dipping series, whose upper 



