476 THE GEOLOGY OF MINNESOTA. 



[Timber. Potsdam quartzyte. 



wheat; but in Martin county corn, stock, and dairying also hold a promin- 

 ent place, as commonly southward through Iowa. 



Both these counties are principally prairie, being natural grassland, 

 without tree or shrub; excepting narrow skirts of timber, which generally 

 surround the lakes and extend along the principal streams, sometimes widen- 

 ing to form groves. Probably the aggregate ai'ea of these belts of timber 

 is less than one hundredth part of either Watonwan or Martin county. 

 The following species of trees, arranged in their estimated order of abund- 

 ance, were noted as occurring on the South fork of the Watonwan river: 

 American or white elm, white ash, box-elder, ironwood, cottonwood, bur 

 oak, slippery or red elm, hackberry, bass, soft maple, black walnut, willows, 

 the American aspen or poplar, and the wild plum. Common species of 

 trees about Silver and Iowa lakes, in Martin county, are bur oak, bass, 

 white ash, white and red elm, and black walnut; bitternut is somewhat 

 frequent; and cottonwood, soft maple and butternut occur rarely. 



GEOLOGICAL STRUCTURE. 



The only exposure of bed-rock in Watonwan county is found, as already 

 stated, in the N. W. of section 29, Adrian. A smooth and flat surface of 

 the very compact and hard, red Potsdam quartzyte is seen here along an 

 extent of five rods from northwest to southeast, with a width varying from 

 five to twenty feet. This is on an eastward slope, in a slight depression of 

 drainage. The quartzyte does not project out of the drift, and cannot be 

 seen at a distance. It is undoubtedly the bed-rock beneath all the south- 

 west quarter of Adrian, but is elsewhere covered within the limits of this 

 township and county by the smoothed sheet of glacial drift, which rises in 

 a broadly rounded ridge because of the prominence of this underlying rock. 

 Through the north half of section 30, Adrian, it lies at no great depth, and 

 has been encountered in ploughing and digging at several places. This 

 ridge, having here and there outcrops of the same red quartzyte, continues 

 more than twenty miles to the west, in northern Cottonwood county. 



In Martin county a large mass of compact, gray sandstone, contained 

 in the till, has been quarried at the south side of Elm creek in the west part 

 of section 6, Rutland, on land of G. S. Livermore of Fairmont, yielding 



