Descriptions of the Exposures. 259 
Descriptions of the Exposures —The four areas into which the 
ledges are grouped are designated as the Portland, Hubbellton, 
Lake Mills and Mud Lake areas. Two of these were recog¬ 
nized by Percival, the third was found by President Chamberlin 
in his study of the region, while the fourth was discovered dur¬ 
ing the course of my investigations. The first or Portland 
area lies within, and upon the eastern rim of the marsh drained 
by the terminal course of Waterloo creek. Rocky Island, its 
most northern exposure, is a ledge arising abruptly within a 
shallow lake at the junction of Waterloo creek with the Craw¬ 
fish river on Sec. 27, Portland township. On three sides the 
bare, polished roc lies moutonnees rise directly from the water, 
but on the fourth margin the gently sloping ledge surface dis¬ 
appears beneath spongy marsh accumulations. The longer 
axis of the outcrop coincides wfith the strike and direction of 
latest glaciation, or S. S. W. This extent is seventy-two rods, 
and its greatest breadth is sixty rods. The highest points of 
its rounded crests are about forty feet above the marsh level. 
No talus nor glacial debris is found adjacent to this ledge, but 
the thin till covering that rests upon the rock surface, bears a 
vigorous forest growth. Its area is approximately twenty- 
five acres. 
A half mile south of this island, domes of quartzite again 
appear along the crest of a ridge eighty feet above the marsh 
level. A succession of these ledges continues along the west¬ 
ern slope and margin of this ridge for a mile, ending in a low 
dome of rock lying in the marsh on the north-east quarter of Sec¬ 
tion 33. These outcrops are all beautifully rounded and striated 
by glacial action, the coincidence of the strike of the beds with 
the direction of latest glaciation, greatly favoring the devel¬ 
opment of these symmetrical forms. The eastern margin of the 
ledge area is heavily overlaid by glacial drift. Along its 
marshy western border are several low mounds of much weath¬ 
ered talus and a wide bowlder fringe, the quartzite blocks lying 
thickly together, and extending for nearly two miles on the lee 
slope of the ridge area. 
On the gentle north slope of the ridge and lying between 
this ledge and Rocky island a very interesting paleozoic con 
