288 E. H. WILLIAMS, JR. — EXTRAMORAINIC DRIFT. 



this time, and that there was do escape of the waters into the Durham 

 valley and the Delaware. A How over that divide would have distrib- 

 uted the clays over the Saucon valley in great bulk. On the Topton di- 

 vide the state of the clay indicates slack water, so that there was no ex- 

 tended discharge over that divide, and any evidence of slight flow has 

 probably been washed away from the steep sides of the Sacony valley. 

 The drainage of the lake was therefore subglacial. 



The clay is generally a reddish brown, unstratified, sandy deposit, with 

 a burden of glaciated, angular and river-rolled material scattered irregu- 

 larly through it. Very few striated stones have been found in the sec- 

 tions studied, and the bulk of the burden consists of river cobbles and 

 pebbles, with a considerable proportion of perfectly angular fragments 

 derived from the rocks to the north of the locality wdiere they occur in the 

 clay. In the case of syenitic fragments, they occur near the South moun- 

 tains, w^here they could have been picked up by shore ice and carried a 

 short distance. The greater proportion of the burden, however, are sand- 

 stones and chert, with a small amount of limestone and slate. The 

 specimen of striated rock exhibited is from the clay, and shows the 

 general freshness of the burden. The slates are generally fresh within 

 if oxidized externally, and workable slate can be found 10 feet from the 

 surface, whereas the average depth of decomporsed soil over an ungia- 

 ciated area, or one exposed to long atmospheric action, is from 60 to 75 

 feet. 



The clay deposit varies from a perfectly clean clay to clayey sand as 

 we go from the deep water of the south to the northern shallows. It 

 is generally unstratified, but shows local areas of stratification. Its 

 thickness varies from a few inches to twelve feet at West Bethlehem, but 

 the general average is three feet. The stony burden thins out along the 

 shorelines and is replaced by the washings of local rocks or of the till 

 left by the ice. Where the clay is stratified it caps stratified sands and 

 gravels, as at Alburtis, of local extent, and due to local variations in cur- 

 rents from the land drainage. 



The Packer clay may have been augmented by slight additions over 

 low levels from dams in the Delaware narrows after the mouth of the 

 Lehigh was free, as there are clays in the Durham valley which are at 

 lower levels than those in the Lehigh and which could have been made 

 by ice-dams in the narrows or by the damming of the valley by the 

 glacier. As soon as the ice freed the mouth of the Lehigh the front was 

 but a few miles south of the great moraine, so that the Packer clays 

 slightly antedated as to their top parts that formation, and the clays in 

 the small valleys from dams in the narrows may have been contem- 

 poraneous. By reason of the recency of the deposits, we can claim that 



