SOUTH MOUNTAIN GLACIATION. 13 



The two parts join at Denville, where the moraine is seen to make a bend at 

 right angles. From the very curve of the eastern part it is evident that a powerful 

 current of ice was poured down the Hudson River region during the period of 

 its formation, carrying the moraine as far as Perth Amboy, which is fully 27 miles 

 south of Denville. 



Southeastern Limit of the glacial Ice. 



The question at once arises whether, during the earlier period of maximum 

 glaciation, the ice extended as far south of the Hudson lobe as it did south of the 

 Delaware lobe. This problem is as yet unsolved. Although many blocks of 

 northern gneiss and trap have been carried across Raritan river, and although 

 white sandstones, conglomerates and quartzites, some of them three feet long, have 

 been carried at least 15 miles southwestward from Perth Amboy, many of which 

 were, as I think, derived from the Hudson river ice-flow, yet, so far as I have had 

 opportunity to observe, they all lie on low ground and are associated with the 

 yellow quartz-pebbles to which I have previously referred. The suspicion there- 

 fore obtains that they were transported by floating ice. 



In the absence of the author the next paper was read by A. A. Wright : 



SOUTH MOUNTAIN GLACIATION 

 BY EDWARD H. WILLIAMS, JUNIOR 



The region studied and concerning which this preliminary note is written is 

 bounded on the north by South mountain just back of South Bethlehem, Pennsyl- 

 vania, and on the south by a spur of the same range south of Center valley, Penn- 

 sylvania. Its eastern edge is on a line through Leithsville and Hellertown, and 

 its western limit is a mile west of Seidersville. It occupies a space three inches 

 from north to south and two in the other direction on the colored map of Lehigh 

 and Northampton counties in Report of Progress, D^, volume i, of the Second Geo- 

 logical Survey of Pennsylvania. An examination of maps 2 and 3 of the Durham 

 and Reading hills, in the same volume, will show that the greater part of the area 

 lies in the Saucon valley, which is landlocked to the south below 400 feet above 

 tide, and which drains into the Lehigh valley at Shimersville by means of Saucon 

 creek. 



The valley is completely surrounded by hills of the South mountain gneiss, which 

 liave a narrow belt of Potsdam about them, while the central part is Siluro-Cam- 

 brian limestone, which has a trend northeast and southwest, and parallel to the 

 trend of the range. The gneiss is generally syenitic in this area, but varies from 

 acid to basic. The limestone readily decomposes to a clay, and in so doing de- 

 velops a finely laminated structure. The Potsdam is a quartzite, with conchoidal 

 fracture, and the latter is due partly to pressure, ]mt generally to concentric aggre- 

 gation about the original grains of the sandstone. It can be usuallv detected when 

 weathered, but when this is extreme it simulates Medina, so that care is neces- 

 sary in determining very much decomposed specimens of both these formations. 



The discussion as to whether ice ever came as far south as Bethlehem induced 

 the writer to put the postgraduates in mining engineering upon this part of the 

 country for their geological survey, and, to make the matter sufiiciently easy of 



