DAYIS: THE HARVARD GEOGRAPHICAL MODELS. 
93 
During the preceding and present cycles of denudation, there 
have been many adjustments of streams to structures, and several 
more adjustments are imminent. The original uplift by which the 
stratified series was given its dip to the west and southwest may be 
assumed to have initiated an extensive system of consequent drainage 
in those directions. To-day, many of the streams flow along the strike 
of the strata, following valleys that have been worn in their weaker 
members, and few streams run down the dip of the monocline. 
Part of this change may be ascribed to the first cycle ; but a 
considerable extension of the change should be referred to the 
present cycle, in which the south-fiowing streams have been greatly 
aided in extending their headwaters by the southward tilting given 
to the region when its present attitude was assumed. The chief 
river of the model is thus seen to follow a subsequent course along 
the basal members of the stratified series. A little further headward 
extension of its drainage area will enable it to divert the upper 
waters of the large river that now flows westward near the northern 
side of the model; the course of this river is about down the dip of 
the monocline from the, older to the newer rocks, and its origin is 
therefore presumably consequent on the uplift at the beginning of 
the previous cycle. The lower beheaded part of a once larger 
consequent river may be seen near the middle of the western border. 
Its former headwaters are represented by certain small streams on 
the older rocks, now diverted to the service of the master subsequent 
river. Several other streams flowing southwest on the older rocks 
near the center of the model also represent the headwaters of a river 
that once escaped across the stratified rocks. They originated on 
the former inland extension of the stratified rocks and flowed down 
their dip to the sea. Now they have become superposed on the older 
rock series, and their former lower trunk is completely lost, owing 
to the successful depredations of the various subsequent streams by 
which the monoclinal valleys are drained. 
All this would be clearer if the successive chapters in the develop¬ 
ment of the region were represented by appropriate models, and 
eventually this may be done; but as the present series is designed 
primarily for school use, it is limited to the exposition of relatively 
simple problems. t 
Various other features of the model might be discussed if time 
and space permitted. The graded lower courses of the streams, in 
contrast to their torrential headwaters; the ungraded outcrop faces 
