BOUXDARY OF THE GLACIATED AREA. 155 



Another noticeable characteristic of deposits over this 

 attenuated border is that the prevailing, highly oxidized mate- 

 rial is mingled with a considerable amount of fresh unoxidized 

 material brought from farther north, showing that the oxidi- 

 zation was mainly preglacial, and that the age of the deposit 

 must be reckoned from the accession of the fresh material. 

 In the effort to determine the age of these deposits from the 

 extent of the oxidization, it also should be ever kept in mind 

 that the ice moved first over an area ^hose surface had been 

 deeply disintegrated and oxidized during the long ages of 

 tertiary time. It was the product of this disintegration which 

 was first incorporated into the mass which was moved along by 

 the ice, and this naturally was carried farthest. The contribu- 

 tions made later were such fresher portions of the rocky surface 

 as had been below the action of the disintegrating agencies of 

 the Tertiary period and so would be mingled with the earlier 

 material wherever the ice overrode the deposits of the primary 

 advance. 



West of the Susquehanna the ice pushed over the plexus 

 of mountains south of Williamsport, rising to a height of 1,200 

 feet above the river and ending along a zigzag line bearing 

 northwestward, as shown in the map, reaching the west 

 branch of the river at Lock Haven. In this area several 

 most interesting and even startling results were produced. 

 Though the ice did not reach the valley of the Juniata River, 

 Professor I. C. White had reported at various places along the 

 border of the river, especially at Huntingdon "great heaps of 

 bowlder trash, both rounded and angular .... and 

 these often very much resemble genuine drift heaps." Some- 

 times these reach an elevation of 100 feet above the river. 

 Later, Professor Williams found unmistakable glaciated 

 stones in the corresponding high level terrace at Lewistown: 

 while on the western side of Warrior's Ridge a little above 

 Huntingdon, where the Juniata cut a narrow gorge through 

 the mountains there was a small deposit of erratics between 

 300 and 400 feet above the river. 



