167 



failed to find any scratches upon their surface, such as are 

 frequently found upon those of the "ground moraine" of 

 this region. They are not of local origin, but consist, in 

 indiscriminate mixture, of granite, gneiss, and slatestoues' 

 from the North. Among these a rose quartz is abundant. 



4. EXTENT OF THE RIDGE. With only such interrup- 

 tions as are made by river valleys and water courses, or 

 by other apparent causes, I have traced this series of 

 ridges, in continuous line, from Wakefield, through Read- 

 ing, North Reading, Wilmington, Ballardvale, Andover, 

 Lawrence and Methuen to Salem in New Hampshire, a 

 distance of nearly twenty-five miles as the bird flies. I 

 have with tolerable certainty identified it on either side 

 of these limits : south, in Melrose and Maiden; north, as 

 far as Derry Station, N. H. 



5. DIRECTION. It will be observed that this line cor- 

 responds with the direction of the glacial strise of this 

 vicinity, about 15 N. W. by S. E. The line projected 

 to the north would coincide with the axis of the Merri- 

 mack valley above Manchester, N. H. 



6. HYPOTHESIS. We have not time to work out the 

 details of the hypothesis which accounts for the facts so 

 far as at present observed. It is sufficient to say that we 

 expect eventually to demonstrate that this net-work of 

 ridges is the medial moraine of that portion of the con- 

 tinental glacier which took its local direction from the 

 Merrimack valley. The floods of water which during the 

 period of its retreat flowed forth from the foot of that 

 glacier would account for the partial stratification that.is 

 observed. 



7. CONCLUSION. But we wait for further investigation, 

 especially in the line north and south. And we solicit 

 facts from any observers, first, as to the composition of 

 the hills in this vicinity, and for twenty miles east or 



