36o FRANK BURSLEY TAYLOR 



In the interlacing series shown in Fig. 9 a considerable 

 number of the morainic deposits and other ice-border features 

 have not been used, as may be seen by comparison with Fig. 8. 

 When these are all studied in their relation to the several mem- 

 bers of the interlacing series, it is found that, with two or three 

 unimportant exceptions, they all fall into line in one or another 

 of the several halting places of the ice-front. Beginning at the 

 southwest with any particular member of the Copake valley 

 series, as for instance No. 6, and going northeast across the 

 interlacing series and noting each deposit numbered 6, the course 

 thus marked out will represent roughly one halt of the ice-front. 

 Then by carefully studying the topography between tongue 

 deposits in adjacent valley series, and allowing for its influence 

 upon the motion of the ice, and making use of all intervening 

 ice-border phenomena as shown in Fig. 8, a fairly accurate 

 restoration of the ice-front at that halt can be made. In doing 

 this the rule outlined above for interpolating around re-entrant 

 angles on mountains or other features with high relief should be 

 followed faithfully. That is to say, in order to restore the ice- 

 front across a mountain ridge between the terminal deposits of 

 two ice-tongues, the tongues having average dimensions for the 

 Berkshire region, allowance should be made for a slope of 100 to 

 no feet per mile along the side of the tongue from its point up 

 to the re-entrant angles on its sides. 



These are the methods by which the remarkably sinuous ice- 

 borders of Berkshire county have been restored, as shown in 

 Fig. 10. The mean course of any one of them represents the 

 general course of the border of the Hudson valley lobe at that 

 halt. These mean lines are bent from a direct course only by 

 the larger features of topography, such as Mount Washington 

 and the higher ranges to the north. In each one of the sinuous 

 lines represented every point projecting away from the ice-field 

 (generally toward the southeast) is an ice-tongue of more or 

 less pronounced development, and every point projecting back 

 toward the ice-field is a re-entrant angle. 



In constructing these lines I have made them continuous 

 where they represent ice-border features actually observed, and 



