522 l^EPORT OF State GEOLOCiisT. 



I'liYsiOiJUArnic features. 



"lliniy important hmd J'onus are wanting in Indiana. There are no 

 mountains!, no valleys formed by upheaval or subsidence, no volcanoes 

 or volcanic rooks except foreign fragments brought by the ice .«heet, 

 no features due to disturbance of the eartli crust except the rock foun- 

 dations of the State itself. 



"nains. — As already indicated, the greater part of Indiana is a plain 

 of accumulation: the surface of a sheet of glacial drift which varies in 

 thickness from a few feet to 500 feet or more. The average thickness 

 is more than 100 feet. It consists chiefly of a mass of clay containing 

 more or less gravel and boulders — the till or boulder clay of the geol- 

 ogists. This is locally varied by heaps, ridges, sheets and pockets of 

 sand and gravel, and in the southern part of the State is overlain by 

 a peculiar fine silt called loess. The l)oulder clay is the grist of the 

 glacial mill, and is composed of a very intimate and heterogeneous 

 mixture of native and foreign materials, containing fragments of 

 almost every known mineral and rock. The large fragments, or 

 boulders, are A\idely distributed, and of every size up to 30 feet in di- 

 ameter. 'J'hey are nearly all igneous or mctamorphic in character and 

 can be traced back to their origin in the Canadian highlands north of 

 the Great Lakes. 



"The driftless area is a plain of dcgradatioiL formed by the removal 

 of the original rock surface to an unkm^vn depth, and now repre- 

 sented by the summits of tlu^ flat and even-topped divides, ridges and 

 hills. 



''Hills. — On the northern plain occur numerous hills of accumula- 

 tion forming the great morainic belts, the result of excessive dumping 

 and heaping up of drift along the margins and between the lobes of 

 the melting ice-sheet. The most impressive examples are found in 

 Steuben, Lagrange, Noble and Kosciusko counties, where they attain 

 a height of "^OO feet or nutre, and are as steep and sharp as the mate- 

 rials will lie. Their peculiar forms and tumultuous arrangement give 

 a striking and picturesque character to the landscape. 



"The Ohio Slope is studded all over with hills of degradation — blocks 

 and fragments of the original plain left by the cutting out of the 

 valleys between them. Some are broad and flat-topped, some narrow, 

 crooked and level-crested, some sharp or rounded, isolated knobs or 

 bnttes. These are very conspicuous in the counties of Greene, Da- 

 viess, Martin, Crawfprd, Orange, Washington and Jackson, but attain 

 their greatest development in Floyd. Clark and Scott, where the 

 Silver Hills and Guinea Hills rise to 400 and 500 feet above the valley 



