192 M. L. FULLER 



are regarded as marking the final passing away of the ice. The ice 

 already reduced to a mere line along the center of the valley could 

 have remained but a short time, and, as the later outlets appear to 

 have been to the north, no further stages of the lake are recorded. 



RETREATAL CONDITIONS. 



Absence of ice-movement. — That ice-movement had ceased before 

 the opening of the lake history of the Stoughton Bay area is clear 

 from the character and distribution of the deposits laid down. 

 Nowhere in the region are there any deposits of the nature of 

 moraines, such as would have been formed at the front of a living 

 ice-sheet. This applies both to the uplands and to the valleys, which 

 are alike free from till accumulations formed either along a gen- 

 eral ice-front or at the terminations of valley ice-tongues. 



The form and structure of the stratified deposits also fail to show 

 any forward movement of the ice-bodies, along the margins of which 

 they were laid down. Folding and faulting of a nature indicating 

 thrusts are absent in all exposures which have been seen, and the 

 ice-contact slopes are practically free from till accumulations, such 

 as would have been formed if the ice had possessed sufficient motion 

 to bring fresh materials to the front. The topographic forms are 

 always those which would result from a receding ice-margin, never 

 from an advancing one. The gradational deposits described on 

 pp. 185, 186 are especially significant in this connection. 



The strongest evidence, however, is from the distribution of the 

 deposits, which, as has been described, form relatively narrow and 

 successive strips along the sides of the valleys, showing conclusively, 

 when examined as a whole, that the ice-shrinkage was not from south 

 to north, or any other fixed direction, but always away from the 

 valley sides. At the latest recorded stage, as shown by the sur- 

 rounding deposits, only a narrow strip of ice remained along the 

 center (Fig. i). Neither this nor the earlier and wider masses pos- 

 sessed the straight or gently curving outlines characteristic of living 

 ice- tongues, but were marked by all the sinuosities and irregularities 

 of an irregularly melting stagnant ice-margin. 



Drainage oj the ice-sheet. — The highest stratified deposits of 

 Stoughton Bay are the Rattlesnake Hill, East Sharon, and Stoughton 



