52 GLACIAL FORMATIONS OF ERIE AND OHIO BASINS. 



be of lowan age covers the Illinoian drift and extends beyond it into the 

 ung-laciated district to an undetermined distance. The early Wisconsin 

 drift is exposed outside the hmits of the late Wisconsin in southeastern 

 Indiana and southwestern Ohio, and may perhaps be represented in the 

 southern portion of the drift east of the reentrant angle in the glacial 

 boundary in western New York. But in central and eastern Ohio and in 

 northwestern Pennsylvania it occurs to but a limited extent, if at all, 

 outside the late Wisconsin. The late Wisconsin drift covers a large part 

 of the glaciated portion of this region. The distribution of its several 

 moraines is indicated on the glacial map. The extent of the great glacial 

 lakes, Maumee, Whittlesey, and Warren, is shown in Pis. XX, XXI, XXIII, 

 and XXVI more clearly than in the glacial map. As the several drift 

 sheets, the moraines, and the beaches are discussed in detail farther on, 

 they may be left here with this passing reference. 



OUTLIISTE OF ROCK FORMATION'S. 



Inasmuch as the topographic features of this region depend largely 

 upon the character of its rock formations, a brief outline of the distribution 

 and characteristics of each of the formations here represented seems necessary. 

 Some difficulty is found in the correlation and grouping of certain formations 

 because of the variations which they display when carried over so large a 

 region, and also because of the uncertainty as to exact equivalency where 

 outcrops occur only in widely separated districts. In some cases a forma- 

 tion whose equivalency is well established has a constitution that is quite 

 unlike its constitution in the type locality. In other cases a similar 

 constitution is found in widely separated areas, but the equivalency has 

 not been fully established. The classification of the Ohio rock series 

 presented by Orton in a recent report of this Survey^ and in the last volume' 

 of the Ohio survey^ is based upon a careful comparison of the Ohio series 

 with those of New York and Pennsylvania, where most of the type localities 

 occur. It is, however, designed only for Ohio, and needs to be supplemented 

 in the wider region embraced in the present report. 



The arrangement of the formations is quite simple, the only axes of 



^The rock waters of Ohio, by Edward Orton: Nineteenth Ann. Kept. U. S. Geol. Survey, Pt. IV, 

 Hydrography, 1898, pp. 638-650. 



^The geological scale of Ohio, by Edward Orton: Geology of Ohio, Vol. VII, 1894, pp. 3^H. 



