hkkshkv.] The River Terraces of the Orleans Basin. 



4.11 



small rounded, pebble-like rock fragments, sometimes only a 

 quarter of an inch thick, have been produced by a dislocation 

 of the bed-rock only amounting to one or two feet. Similar 

 clay seams containing- rock fragments mark the veins where 

 the pressure was not too great. In the latter case all the rock- 

 was crushed and the clay selvages, or "gouges," of the ordinary 

 mineral veins resulted. 



Where a very large landslide moved a long distance down 

 a mountain, over a variety of rock formations, the clay at its 

 base may be very thick, the included smooth rocks may be of 

 considerable variety, and the harder may have scratched the 

 softer. If, then, erosion removes the landslide deposit down 

 to this clay base, there is danger of the latter being discriminated 

 as an old glacial deposit. If I remember rightly, I once exam- 

 ined such pseudo moraines (old landslides) in the Black Hills 

 of South Dakota, and subsequently a geologist who was not a 

 glacialist described them as evidences of glaciation. 



In the Orleans region I find that the scratches on stones 

 in the landslides are less distinct and much less numerous than 

 in the undoubted glacial deposits, and the composition of the 

 former indicates a more local origin for the material. After 

 examining a great number of landslides. I find that the diffi- 

 culty of discriminating them is greatly lessened. In the case 

 of the deposit at the mouth of the North Fork of Pearch Creek, 

 the great variety of rocks present, the beautiful and abundant 

 striation, the character of the clay base, and the inclusion of 

 logs point strongly to a glacial origin. 



A few hundred feet farther upstream, on the opposite side, 

 there is a terrace-like remnant of the same deposit, rising fifty 

 to sixty feet above the creek, which latter has evidently cut at 

 this point a post-glacial canon in till, 100 feet wide and fifty 

 to sixty feet deep. The slopes above are extremely rugged and 

 present no evidences of glaciation. Thence to the head of the 

 creek, the stream flows in a narrow rock canon abounding in 

 falls ten to twenty feet high. If one keeps in this canon, near 

 the creek, he sees -no evidences of glaciation. But, curiously, if 

 he will climb up the slopes at almost any place, at the height 

 of 100 to several -hundred feet, he will find a strip of bouldery 



