296 E. H. WILLIAMS, JR. — EXTllAMORAINIC DRIFT. 



tain. Sections at Alburtis (420 feet) and Trexlertown (370 feet) sliow 



similarity of deposits as follows : 



A lb I i ) i is. Trc. * -lerto wn . 



Unstratified red clay oO inches. 



Stratified sand and clay 27 inches. 10 " 



" clean clay, jointed when dry 7 feet. 16 " 



" clay and gravel with rolled limonite 31 •' 4 feet. 



Till with cobbles and bowlders of Oriskaiiv, etcetera ... 10 " 11 '' 



./ ' 



The difference between the nine feet of Packer deposits in the mid- 

 valley and the thirty-nine feet on the shallows bordering the Archean 

 highlands is caused by the drainage from the latter, as the watershed is 

 two miles back of Alburtis, and the amount of water precipitated was 

 considerable. Instead of a cutting down of the country since glacial 

 times, therefore, we find that the pregiacial surfaces are generally covered 

 by a clay cap, or an accumulation of gravel, and Professor Prime's theory 

 is fully proven. 



Summary. 



The clays are the work of ice in slack water, and thus far no signs of 

 life have been found in them ; they were deposited immediately after the 

 retreat of the ice, and the oldest are at the western part of the lake ; 

 their burden and that of the till shows recency of formation, as do the 

 outcrops. We may conclude that the great moraine was formed imme- 

 diately after the Avithdrawal of the ice from the Lehigh, and that it and 

 the extramorainic dej^osits of the region were part of the same ice-inva- 

 sion, which w^as of recent age and short duration. 



