156 Transactions of the Canadian Institute. [Vol. VII. 



removed according to circumstances. Eventually, there would be a 

 uniformly graded slope from stream bed to mountain top (AGCDHF). 

 After the production of this slope the process will continue, but more 

 slowly, with the gradual reduction of the crest, and corresponding 



Figure 8. 



decrease in grade, approaching but never reaching complete horizon- 

 tality. Of necessity there will always be one point, or a series of points 

 in line, higher than all the rest. From here the gradient would be 

 downwards in all directions. In the late mature stages, when there is 

 some approach to a nearly smooth surface over the whole mountain^ 

 there will be no abrupt change in slope. 



Such an explanation of the process of degradation makes no pro- 

 vision for the occurrence of areas of greater or less extent with almost 

 identical elevation, (A' IC, DK) ; nor for the abrupt changes in gradient 

 such as occur at the shoulders before mentioned (A', C, D.) Hence, in 

 the writer's conception of the process, it seems inadequate to explain 

 significant facts of the present case. 



The two-cycle (n+ i cycle) h}-pothesis would explain these peculiar- 

 ities by postulating a previous cycle (or cycles) of erosion in which the 

 land was cut down to a surface of very faint relief and subsequently 

 elevated and dissected, the new valleys not having yet extended their 

 graded slopes far enough to completely obliterate the plain of the 

 former cycle. The shoulders were produced where the change in 

 gradient from the present valley side to the older plain occurs. 



In almost every locality where the Cambro-Silurian sediments are 

 seen in contact with the crystallines, the surface is seemingly quite 

 fresh. Except in one known locality, where a distinct arkose of angular 

 material is found, the old soil cover seems to be completely gone. The 

 process by which this cover was removed and the surface of the Archean 

 freshened, is at present undetermined. 



Summary. — The present topography of the pre-sedimentary floor 

 may be regarded as the product of a degradation which produced a 



