PEMBROKE RIDGES.- 687 



to the complexity of the range. The portion on the north side of Tona- 

 wanda Creek hes within the hmits of the Medina quadrangle and occupies 

 the interval between the creek and a marshy tract nearly parallel with it a 

 mile or so to the north (see PI. III). The most jjrominent group of knolls 

 in this part of the range bears some resemblance to an esker, in that it 

 trends directly across the range and has a sharp, narrow gravel ridge. The 

 ridge has not, however, so smooth a crest and slopes as generally characterize 

 eskers. The north end rises abruptly to a height 130 feet above the bor- 

 dering marsh, but most of the ridge is only 75 to 90 feet above the marsh. 

 It is about a mile in length and is narrow and sharp throughout its course. 

 The knolls around this esker-like ridge are generally but 20 to 30 feet high, 

 being less prominent than in the part of the range farther west, on the 

 south side of Tonawanda Creek. 



The range standing south of Indian Falls is less than a mile in length 

 and scarcely one-fourth mile in width, but stands nearly 50 feet above 

 bordering tracts on the south and east, and even more above the tract on the 

 north. From this range southward to the main range there is a gently 

 undulating strip strewn with bowlders, that separates the old lake plain on 

 the west from a shallow bay on the east which occupied 3 or 4 square miles. 



STEUCTURE OF THE DRIFT. 



So far as can be ascertained from the surface ditches and shallow 

 excavations, these ranges of knolls are composed of gravelly and sandy 

 material with but little clayey till. They are in striking contrast to the 

 Alden and Marilla moraines, which, as above noted, are composed largely 

 of clayey till. There are numerous surface bowlders, but there seems not 

 to be many bowlders incorporated in the di-ift. 



The cause for so much water action in connection with the production 

 of this moraine is not apparent. It does not seem due solely to its having 

 been formed near the level of Lake Warren, for in that case we should 

 expect the Alden and Marilla moraines to show evidence of more water 

 action. 



OUTER BORDER DRAINAGE. 



There is a sag along the outer border of the south range extending 

 from its western end at the shore of Lake Warren eastward nearly to 

 Batavia, which aifords adequate room for westward discharge of glacial 



