201 
Perhaps I may remark before closing this brief paper that I 
am not unaware that flint implements of palaeolithic type have 
been discovered in the valley of the Delaware, in the United 
States, by Dr. C. C. Abbot, which have been referred to the 
Glacial epoch. 
With regard to these, a thorough examination and study of 
the gravels in question have been recently made by Mr. Henry 
Carvill Lewis, of the Second Geological Survey of Pennsyl- 
vania, and a paper on the subject was read by him before the 
Mineralogical and Geological Section of the Academy of 
Natural Sciences of Philadelphia, November 24th, 1879. 
It appears from this examination that the Trenton gravels 
in which the alleged implements were found are the latest 
of four gravel beds in the valley of the Delaware. The forma- 
tions of this region are divided into five clays and four gravels, 
which, beginning at the oldest, succeed each other as follows : 
1. Jurasso-cretaceous plastic clay; 2. Tertiary clays (Brandon 
period) ; 3. Bryn Mawr gravel (Upper Tertiary) ; 4. Branch- 
town clay ; 5. Glassboro gravel (Pliocene) ; 6. Philadelphia 
Note.— T he blocks of the illustrations have been kindly lent by Messrs. 
Triibner & Co. 
P 2 
