644 PROCEEDINGS OF THE BALTIMORE MEETING 



West and South quarries bears stria? reading south 60 degrees west ; these are 

 intersected by lines south 85 degrees west. 



On Point Pelee island the older sets range about south 60 degrees west, 

 while the more recent are east-west. 



Perhaps neither of these two sets of striae represents the movement of the 

 general ice-sheet during either the advancing or the maximum stage ; it is 

 more probable that all this scoring is the work of the glacier after it has 

 ceased to advance. Whatever grooving and polishing had been accomplished 

 by the ice at earlier stages was either modified or obliterated by the action of 

 the Erie Lobe stage, when the Erie basin was occupied by a deploying lobe of 

 ice. In this area, then, constancy in direction of stria? would be found only 

 along or very near the axis of the lobe. Laterally from this axis the earlier set 

 would be more generally east-west, but as the front of the ice successively 

 took new positions the last movement over a given place off the axis was out- 

 ward from the axis, thus imposing on the east-west set stria? trending to the 

 north or to the south. The Erie lobe was associated with ice from the Labrador 

 dispersion center. The general motion of the ice through this basin should, 

 therefore, be south of west. The fact that we have some readings north of 

 west, and many readings more nearly east-west, indicates that the Erie Lobe 

 axis was a little south of Kelleys island. On this supposition, then, the east- 

 west readings and those approximately east-west represent the more general 

 motion of the Erie lobe, whereas the other readings are due to the deployment 

 at a later stage. 



The more vigorous scoring, particularly the grooves, shows less diversion 

 from the east-west line. 



Some of the surfaces from which these readings were taken are so com- 

 pletely covered with very fine scratches that one can not state with absolute 

 certainty the order in which the stria? were made. 



The Deep Grooves 



A cross-section of this grooved surface (figure 1, plate 109) is a half -oval 

 figure. The apex drops off into the quarry ; therefore the original shape of the 

 cross-section can not be given. The outline preserved suggests somewhat the 

 roche moutonnee type of erosion surface. 



The prevailing cross-section of the individual grooves is U-shaped. The 

 grooves are sharply defined, almost mechanically precise in outlines. The 

 north side of one of the grooves overhangs. On all of the surfaces, both in 

 the grooves and on the areas between the grooves, are delicate stria?, with 

 only now and then a harsher line. There is very little evidence of chatter 

 abrasion, and only one conspicuous gouge was noted. Plate 110 shows an area 

 where the tools diverged from the straight line and produced a fluting effect ; 

 the rock surface around which the tools moved appears no harder than the 

 rock elsewhere. 



. A simple explanation for these great grooves, one that is not uncommonly 

 given, is to account for them by the lathe-like effect of the large boulders held 

 in the bottom of the ice. A closer analysis, however, leads to the following 

 conclusions: (1) The vigorous scoring indicates a localization of tools and a 

 constant supply of them in the basal area of the ice ; the source of this supply 



