1913] The Moraine Systems of Southwestern Ontario. 63 



line running southwest from London the ice of the Huron and Erie lobes 

 met head on. This produced a dead line in the ice and a trough or crease 

 in its surface. This crease led southwest from London to the edge of the 

 ice sheet and was the only possible way of escape for the water that 

 flowed into the depression of "Ontario Island". Judged by its hydro- 

 graphic basin, that river, which we may call the "Crease River", should 

 have been a river of large size. It was the glacial precursor of the modern 

 Thames River. 



There are several interesting facts bearing upon the existence of 

 this glacial river beyond the boundaries of Ontario. The details cannot 

 be given here, but it may be said that a great river issued from the ice 

 sheet in central Indiana at and for some time after the maximum of the 

 ice. This river came abruptly from the ice and carried no sediment. 

 Remembering that the depression in the surface of the ice sheet existed 

 over "Ontario Island " before the island itself was uncovered, it is evident 

 that the "Crease River" at that stage encountered no dirty ice and 

 gathered no sediment. It issued at the ice front as clear water. When the 

 ice front had retreated to a position marked by a moraine which passes 

 through Defiance, Ohio, a river issued from the ice which brought an 

 immense quantity of sand, enough to cover the greater part of Fulton 

 county, Ohio. No earlier deposit of this kind is known, and it is believed 

 that the deposit mentioned marks that time when the Crease River 

 first encountered dirty ice; that is, when the kames northeast of Strat- 

 ford were made, which was just before the uncovering of "Ontario 

 Island". At this time there was probably a continuous narrow trough 

 and a gradual descent from Stratford to Fulton county, Ohio. A little 

 later, when the island was first uncovered, its surface near London was 

 probably covered by a shallow, temporary lake which stopped the 

 escape of sediment, and the ice lobes soon after pulled apart so as to let 

 the water of glacial Lake Maumee nearly up to London, and then the 

 gravels were deposited in it, as may be seen in the great gravel beds near 

 Komoka, a few miles west of London. Curiously enough, in the un- 

 covering of "Ontario Island" the first part to appear above the ice was not 

 the highest part of the highland, which is located not far from the village 

 of Dundalk, but was a long, flat area extending from the city of London 

 at least 60 or 70 miles toward the northeast with a width of 10 to 20 

 miles. This area formed a low-lying flat island in the midst of the ice 

 field and was more than 100 miles from the nearest part of the mainland. 



With continued recession of the ice, the front drew back on all sides 

 enlarging the area of the island. But the separation of the two lobes 

 did not increase the land surface southwest of London, because glacial 



