46 LOWER PENINSULA. 



coarse-grained, gray dolomitic rock identical with the dolomite rock 

 in the sink-hole on Mr. Marston's farm. The horizon of all these 

 rocks seems to be below the strata of Thunder Bay River near 

 Trowbridge's mill. For a circle of many miles around the lo- 

 calities described, rock beds of the same horizon seem to 

 occupy the surface, covered by a more or less considerable coating 

 of drift material. The drift soil of this region is a fertile, gravelly 

 loam, which was densely covered with forest until a number of 

 years ago fires swept through them, totally destroying them for 

 many square miles. By this clearance of the productive soil, nume- 

 rous settlers were attracted to the spot, whose fields have now a 

 really promising aspect. Wheat, oats, grass, and potatoes give 

 very good crops, which, from the vicinity of the lumbering districts, 

 always find a ready market and good prices. Mr. Johnson told 

 me he raised for three successive years nearly a hundred bushels of 

 oats from an acre of land. I saw some of his oats, which were 

 heavier than any I had seen before, and certainly, even if the hun- 

 dred bushels to the acre were a slight exaggeration, indicated 

 much fertility of soil. An interesting feature of this district are 

 the numerous sink-holes found in it, hundreds of which may be 

 counted along the headwaters of Thunder Bay River ; some are 

 small, funnel-shaped depressions, dry on the bottom, or containing 

 waterpools ; others are narrow, vertical clefts, described to me by 

 the woodsmen as sometimes 80 and 100 feet deep ; and it is 

 said of one Avhich I passed that a large stream of water rushes 

 across its bottom. A few of these sink-holes, as mentioned before, 

 are of very large size, and form lakes. One of the latter is Sunken 

 Lake in Township 33, R. 6, Section 32. It is about one mile and 

 a half long, and in its widest part 500 yards. During the wet season, 

 it is filled with water, having a depth of 90 feet ; its overflow forms 

 a branch of Thunder Bay River, which at that time is used for float- 

 ing logs from the surrounding pineries to the saw mills of Alpena. 

 During the dry summer season, the water almost totally disappears 

 from the lake, making its escape through the rock crevices in its 

 bottom. Formerly the water flowed off very rapidly, making a 

 strong whirlpool. The lumbermen, in order to keep the water in 

 the lake, threw masses of brush and even whole trees and rocks 

 into the crevices to stop them up, and partially succeeded, but the 

 water soon again cleared its passage through those obstructions ; 



