NATURAL HISTORY AND PHYSIOGRAPHY OF NEW BRUNSWICK. 209 
these valleys originated on a southeasterly sloping surface as it 
arose from the sea. Had the underlying rocks been uniform in 
texture and hardness, those rivers would doubtless have kept 
those courses to the present day. But the rocks were not of equal 
hardness, but on the contrary consisted of bands of harder and 
softer rocks running for the most part directly across the courses 
of these rivers. In the process of erosion these softer bands were 
cut down rapidly, forming large right-angled branches to the 
older valleys. Ultimately these branches were able to cut back 
into neighboring valleys and frequently to capture their head 
waters. It is in this erosion by branches of the main valleys along 
the softer rocks crossing from valley to valley that we have the 
explanation of the changes which have altered the original 
arrangement to the conditions that we find at the present day, for 
all of the river courses of this system seem to lie either in the 
ancient northwest and southeast valleys across the rock bands, or 
in northeast and southwest valleys following the general direction 
of the softer rocks. 
Turning to these cross valleys, we note that by far the most 
important of them is the Oromocto, which lies near the middle 
of the broadest of the bands of the soft Carboniferous sandstones. 
Starting as a small branch of the Keswian River (which itself, 
running across a greater extent of soft rocks that any of the rivers 
to the westward, cut its channel more rapidly than they, thus be- 
coming a sort of trunk river), it cut backward into the Rusagon- 
ian valley, capturing its upper part. It is precisely because this 
valley was the first thus to be captured that it is now the least 
distinct of them all (especially east of its captor). The Oromocto 
then extended farther back capturing a branch of the Nerepisian 
valley. Similarly, but somewhat later, a branch of the Nerepis- 
ian, eroding backward (along the present Shin Creek), captured 
the Upper Leproian, but the final capture of two branches of the 
Magadavian was only effected (as Note 73 shows) by aid of the 
glacial period. Meanwhile, and very early in this series of 
changes, certain bands of soft rocks occupying the present Belle- 
isle-Long Reach and Kennebecasis valleys (their presence there be- 
ing due to earlier geological causes worked out by our geologists) 
