650 GLACIAL FOR]VIATIONS OF ERIE AND OHIO BASINS. 



Basins lying' within the moraine, such as that of Lake Chautauqua, seem 

 also to mark places where the ice remained for an exceptionally long time. 

 Many of the lake basins in the moraine are, however, due to irregularities 

 in the drift surface which may not be easily explained. 



INNER BORDER PHENOMENA. 



Between the Cleveland morainic belt and the next later morainic sj^stem 

 there is a tract Avith smooth or very gently undulating drift surface and with 

 rarely a knoll worthy of note^ the tendency toward aggregation in knolls 

 being much less than in the district outside the Cleveland belt. 



No strise have been observed except in Wayne Township, Ashtabula 

 County, Ohio, Avhere a sandstone is glaciated. Their inconspicuousness is 

 due probably to the rapid weathering of the shale which imderlies the 

 greater part of the district. 



The thickness of the drift in the valleys is known to be A^ery great, 

 for wells seldom reach the rock, but the uplands and slojjes are thinly coated 

 with di'ift, the depth seldom exceeding 25 feet. 



POSTGLACIAL RIDGES. 



A network of recently formed ridges in Cuyahoga shales occurs in 

 western Trumbull County, Ohio, near the "Old Brick hotel," about 2 miles 

 northwest of BraceAdlle. They are on a lowland tract, the greater part 

 of Avhich is A^ery level, but at the northwestern end of the system of ridges 

 there is an ascending slope on Avhich one of the ridges is developed. The 

 area over Avhich they were obseiwed scarcely exceeds 10 acres, but since a 

 complete tracing of them was not attempted they may have a greater 

 extent. Their usual height is 3 to 6 feet, and their breadth about 100 feet. 

 In form they bear a striking resemblance to low eskers, but in structure they 

 are very different, being composed of rock instead of drift. The shales 

 which constitute them arch Avith the surface of the ridges, and become hori- 

 zontal on each side within a few feet of the base of their slopes. The cross 

 section of one of them is well shown on the north side of the State road, 

 AAdiere an artificial ditch is opened through it. The ridges are usually joined 

 together, but a single isolated one being observed. They meet at various 

 angles, but are all nearly straight. The prevailing trends are north to south 

 and east to west, but some have a trend N. 30^ W. to S. 30° E. The one 



