PAPERS ON GEOGRAPHY AND GEOLOGY 181 



GLACIAL PHENOMENA IN THE VICINITY OF 

 CARBONDALE 



J. E. Lamar, Illinois State Geological Survey, Urbana 



The area particularly discussed in this paper is that of 

 the Carbondale quadrangle, in the northwest comer of 

 which the town bearing the same name is located. This 

 quadrangle may be roughly divided into three topo- 

 graphic units according to the bed rock formations which 

 underlie these units respectively, as shown in the accom- 

 panying figure. The northern unit is that underlain by 

 the Carbondale formation, composed of sandstone and 

 shale, which when eroded, gives rise to a gently rolling 

 surface. The central unit, which is by far the largest 

 of the three, is underlain by the massive sandstones and 

 shales of the Pottsville formation. This part of the 

 quadrangle is very rugged and constitutes a portion of 

 the Illinois Ozarks. Sandstone bluffs and cliffs are 

 numerous. The southern unit of the quadrangle is that 

 underlain \)j the limestones, shales, and sandstones of 

 the Chester group. It has a varied topography. In 

 places it is like the northern unit, and elsewhere like the 

 central unit, particularly in the areas where some of the 

 prominent cliff -forming sandstones are well developed. 



The north three-fourths of the quadrangle drains to the 

 north; the south one-fourth to the south. The north- 

 ward drainage eventually merges in Craborchard Creek, 

 which flows westward across the northern part of the 

 quadrangle, but turns abruptly to the north in the north- 

 west corner to join Big Muddy River. 



The Illinoian glacier spread over the northern half of 

 the region just described. It came dominantly from the 

 north and perhaps a little from the east. The ice of the 

 glacier was probably porous and much crevassed from 

 the buffeting against the hills of the country over which 

 it had passed, and its advance was seemingly very slow. 

 The rapid melting and pronounced deposition which ac- 

 companied the formation of the terminal moraines of the 

 Wisconsin ice were essentially missing. The melting of 

 the Illinoian ice seems to have been comparatively slow. 

 The ice moved over the rolling topography of the north- 



