312 



CAPE COD GEOLOGY 



from the sea, especially on its southeast side, and then more gently toward its 

 middle rolling hills. The axial ridges become lower toward the southwest in the 

 direction of their length, and are discontinuous, but their massiveness is dis- 

 proportionate to the details, such as the bouldery ridges, and the kettle holes 

 which here and there interrupt the surface, and which were formed by the 

 action of ice. 



KETTLE HOLES 



The kettle holes on Naushon are typical morainal features and they were 

 probably produced by the melting of buried blocks of ice or of outlying parts 

 of the ice front that were encumbered by drift. They have been mapped in 

 detail by Mr. B. F. Koons. 1 



Most of the kettle holes are in the morainal upland and show no relation 

 to the ice front and no alignment of their longer axes to the direction of the 

 motion of the ice. In the middle of Naushon there is a crowded group on the 

 northeast side of the large ("Grinnell") swamp, which is an extension of the 

 depression forming Tarpaulin Cove. Many of the kettle holes are occupied 

 by small pools or swamps. Mary's Lake, at the east end of the island, is a deep- 

 sided kettle hole, from which an ice block has melted out. The depth of some 

 of these ice-block holes would seem to indicate the deposition around their 

 sides of the sand and gravel that underlie the till. In a frontal moraine that is 

 subject to the pressure of ice, blocks of ice may behave very much as large 

 boulders and may become so much involved in movements of the ice sheet and 

 the underlying terrane as to assume forced relations with older displaceable 

 material. Ice blocks evidently lay out in old channels or shallow valleys on the 

 south side of Cape Cod and were surrounded and probably covered by deposits. 

 The glacial trough on Naushon that extends from French Watering Place inland 

 to the west side of Tarpaulin Cove is the site of a remnant of ice, signs of which 

 are shown in the swamp and central lakelet near its east end. On Cape Cod 

 the blocks of ice that gave rise to kettle holes in the outwash plain and in the 

 moraine, as at Brewster, were remnants of the sheet that advanced to the 

 outer line of islands. The same conditions doubtless prevailed on Naushon and 

 the Gosnold islands generally, so that the ice blocks were worked over by the 

 front of the ice when it lay along the crests of these islands. 



1 Koons, B. F., Upon the kettle holes near Woods Hole, Mass., Am. Jour. Sci., 3d ser., 27, pp. 26- 

 264, 1884. Also additional notes on the kettle holes of the Woods Hole region, Mass., Am. Jour Sci 

 3d series, 29, pp. 480-486, 1885. 



