MEETING, MONDAY, APRIL 3. 73 



but a slight deflection of the ice-front to the south. The 

 same is true where the moraine crosses the valley of the 

 east branch of the Susquehanna. The grand deflection of 

 the line to the northward is evidently due to variations in 

 the forces which were pushing from behind. 



Now that an accurate knowledge of the southern limits 

 of the continental glacier is being obtained, it will be 

 possible to get a variety of approximate estimates of the 

 quantity of erosion which has taken place since the great 

 ice age, and so a more correct idea of its antiquity. 

 A full account of this subject will appear in the Re- 

 port of the Pennsylvania Geological Survey. Arrange- 

 ments are in progress for Mr. Wright to continue the 

 exploration through Ohio during the coming summer of 

 1882. 



The remarks of Professor Wright, illustrated by refer- 

 ence to the great, original map above alluded to, were heard 

 by an appreciative gathering, who also examined with in- 

 terest, a dozen or more specimens of the "scratched stones," 

 showing glacial action, as well as some of the palaso- 

 lithic implements exhibited by the speaker. At the close 

 of his address a discussion arose between the Rev. R. 

 Randall Hoes, of Lambertville, near Trenton, N. J. (who 

 happened to be in town, engaged in some genealogical 

 research, and knew the locality well, having a large col- 

 lection illustrating the mineralogy and ethnology of the 

 region on his own shelves), tlohn H. Sears of the Peabody 

 Academy of Science, Prof. I. J. Osbun of the State 

 Normal School, and Professor Wright, in which some 

 difierence of opinion was developed as to the power of 

 running streams to cut their way down through obstruc- 

 tions of stone or gravel, and as to the rate of cutting. 



ESSEX INST. BULLETIN, VOL. XIV. 5* 



