359 [Shaler. 



origin. AlthoLigli limited within the regions which have been covered 

 by the glacial mass, these basins are not equally distributed over all 

 portions of those areas. They are largest, deepest aud most numerous in 

 those portions where we have reasons for concluding that the glacial 

 sheet was thickest, and diminish as we approach the southern bound- 

 ary of the ice field. They arc less conspicuous and cease to be no- 

 ticeable before we reach the limits of the glacier as shown by scratched 

 and polished surfaces. There seems to be some reason why the surface 

 of a country underlaid by little disturbed sedimentary rocks should 

 present a less favorable field for the formation of numerous basins, 

 than where the underlying rock has been rendered varied in structure 

 by irregular metamorphism and injected materials. Until, however, the 

 precise character of most of our lakes is ascertained, and it is deter- 

 mined whether they are rock basins or only moraine lakes, it will not 

 be possible to attach much importance to this point. 



There are coincidences in the figure of these basins which have the 

 highest value. Few, except the smallest, present any approximation 

 to a circular figure, and in a general way the larger the area the 

 greater the proportionate extent of the major axis. If we could ac- 

 cept the gradations in size as degrees of development, then it would 

 seem likely that the force producing these basins acted in such a man- 

 ner that, if originating in a circular depression, they necessarily be- 

 came elongated and tended to develop the greater diameter more 

 rapidly than the lesser. This feature has an additional value when 

 we notice that the major axis of the basins has usuallv a north and 

 south trend. There are very conspicuous exceptions to this law to be 

 found outside of the surface of New England, but in them as well, 

 there seems to be a general rule that, failing to follow the usual north 

 and south direction, their major axes have a direction corresponding 

 to that of the river system or valley in which they are situated. The 

 most conspicuous lake basins which do not seem reconcilable with 

 either of these divisions are those of Athabasca, Slave and Great 

 Bear lakes, which, as will afterward appear, are explicable if we grant 

 that the continental glacier had little or no southward movement in 

 such high latitudes, but that the accumulation of ice fuand escape in 

 an easterly direction. 



In the great depth of these basins, compared with their other di- 

 mensions, we have a feature which needs to be borne in mind while 

 seeking an explanation of their for.nution. Many of the smaller ba- 

 sins have the vertical bearing so great a proportion to the horizontal 

 measurements as to put at once out of the question that theory which 

 derives them from the ordinary irregular wearing at the base of a 

 glacier. Great as this depth fre(|uently is, it must be remembered 

 that when the basins were formed it must have been far jrreatcr. If 



