1876.] 51 [Wright. 



" till " of the region. Considerable difficulty, at first, attended the 

 work of tracing the system, from the fact that spurs frequently run 

 off from the main line and disappear. This occurrence is likely to 

 deceive the inexperienced investigator into concluding that the whole 

 series has terminated. Furthermore, extensive swamps and small 

 lakes repeatedly occur in the reticulations of the series, while also 

 the underbrush greatly impedes progress. Still again, for causes 

 known and unknown, there are frequent interruptions of the series. 

 Streams have cut through it. The Merrimack Valley crosses it 

 nearly at right angles. Villages and cities have been built at various 

 points along the course of the series, as at Ballard Vale, at Wake- 

 field, Lawrence and Methuen, where men have been at work for a 

 generation in removing the material for paving streets and ballasting 

 railroads. Sometimes the ridges disappear in a sandy plain, in which 

 case, however, there are usually bowl-shaped depressions in the plain 

 along the line of general direction. This is noticeable east of Bal- 

 lard Vale. It is quite possible that at other places the ridges are 

 buried in a peat bog. Other interruptions may be accounted for by 

 the unknown action of the currents of water which accompanied the 

 disappearance of the continental glacier. I have now traced the 

 course of the series which passes through Andover, south through Bal- 

 lard Vale, past Foster's Pond and Martin's Pond, along the Town line 

 between Wilmington and North Beading, across the Ipswich River 

 two miles east of Wilmington, through the eastern part of Reading, 

 and near the line between that town and Lynnfield, to Wakefield, 

 thence onward with more or less certainty to East Maiden. North- 

 ward from Andover it crosses the Lowell and Lawrence Railroad, 

 about a mile west of South Lawrence, and comes down to the inter- 

 vale of the Merrimack, opposite the new water works. It is seen 

 like a Chinese wall ascending the reservoir hill on the opposite side 

 of the river. Thence it passes in unbroken line northward to Me- 

 thuen. Scattered portions appear west of the Manchester and Law- 

 rence Railroad, as far as Messer's Station. 1 The extreme distance 

 between the points here mentioned is nearly thirty miles. But more 

 decided indications in Methuen are seen farther west, northward from 

 Crystal Pond, and still again, a half mile west of Salem Station, 



*See Plates II and III. In Plate II the degree in which the ridges are independ- 

 ent of the river valleys is seen ; also the relation of the series to the large rounded 

 hills, as in Lawrence and Ballard Vale. In the latter place there is a typicul ex- 

 pansion of a portion of the series into a plain with bowl-shaped depressions. 



