366 GEOLOGY. 



and about as wide at one point as at another. If the margin remained 

 constant in position, but bore unequal amounts of material at different 

 points, the moraine would be unequally developed. Where there 

 was much material it would be higher and probably wider than where 

 there was but little. Irregularity of height and width would thus be 

 introduced by reason of the unequal amounts of material at different 

 parts of the ice edge. 



If, instead of remaining stationary, the margin of the ice; moved 

 alternately backward and forward within narrow limits, the effect 

 would be to spread the moraine by widening the zone of submarginal 

 accumulation. If, during the oscillation of the margin, it remained 

 stationary either during or after its minor recessions or advances, or 

 both, subordinate ridges would be developed, marking the positions 

 of the several halts. If the edge of the ice remained parallel to itself 

 as it advanced and receded, these subordinate ridges would be parallel, 

 and each a miniature terminal moraine. But if while the edge of the 

 ice was carrying unequal amounts of material, its edge oscillated 

 unevenly, with halts, that is, if recessions and advances were unequal 

 at different points, the several subordinate ridges formed at the vari- 

 ous positions of halt would not be parallel, and would not be equal 

 in height or width, and no one of the ridges would be uniform in size 

 throughout its course. Adjacent ridges might touch each other at 

 some points, and be separate from each other by considerable intervals 

 at others. The result would be a series of interlocking moraine ridges 

 of variable heights and widths, constituting a " tangle " of moraine 

 hills and ridges, with depressions of various shapes and sizes. In this 

 way it is believed many of the characteristic hills and hollows of ter- 

 minal moraines arose. If marginal masses of ice were detached from 

 the main body during its temporary recessions, they might subse- 

 quently be buried by deposits of drift. Later, when these buried 

 ice-blocks melted, a kettle-like depression, marking the site of the 

 buried ice block, would result. Thus would be added another ele- 

 ment of complexity in the topography of the terminal moraine. Such 

 surface debris as there may have been on the ice while the edge was 

 stationary was continually being dropped (dumped) at the edge of 

 the ice. If the edge of the ice oscillated, this drift would have been 

 scattered over a zone as wide as the zone of oscillation. "Wherever 

 and whenever the edge remained perfectly stationary, there was a 



