150 NEW YORK STATE MTSEUM 



size of stream, the rocks stand on edge and run parallel to the 

 supposed course so that this structural influence is toward a nar- 

 row and reasonably straight gorgelike form. It is not only pos- 

 sible that the gorge is narrow, but even probable that it is narrower 

 than the present ^loodna, i. e. less than 100 feet wide. 



How deep such an inner gorge may be if it does exist is a prac- 

 tical question in tliis particular case, because its depth has a direct 

 influence on choice of depth of pressure tunnel. Because of the 

 evident narrowness it is likely that it is not of very great depth 

 — in view of the quaHty of these shales perhaps not over a hun- 

 dred feet. 



Is there any one point more than another favorable for such a 

 notch? There are two facts bearing on this question, (i) the vari- 

 ation in core saving which indicates that hole no. 5/A44 with 

 yi has a recovery of only 1/5 the average, and (2) the fact that 

 hole no. 15 A44— , which is the next hole, shows the lowest bed 

 rock in this valley. On the ground of profile therefore and on the 

 ground of structural weakness there is reason to choose this space 

 between no. 5 'A44 and no. 15 '.-\_14 as the most likely position. 



Summary. The very abnormal profile of the ^loodna valley 

 based upon the borings m.ay be due either (i) to parallelism with 

 the stream course, or (2) to a graded condition of the stream in 

 some preglacial epoch, or (3) to modification of an original less 

 prominent channel by ice erosion. 



It is the opinion of the writer that the ancient stream crossed the 

 profile line much as the present stream does, that the additional 

 narrower valley immediately to the west side is that of a pre- 

 glacial tributary instead of a bend of the Moodna itself, that there 

 was a development of a moderate sized somewhat flattened valley 

 corresponding to the benches and shelves noted in other streams, 

 including the Hudson, that subsequent elevation of the continent 

 rejuvenated the stream which cut a deeper narrow inner notch, that 

 glacial ice moving in reverse direction widened and smoothed this 

 upper portion of the valley, but that there may yet be a remnant 

 of the deeper notch in its bottom, and that the space bet\veen holes 

 no. 5 'A44 and no. 15 'A44 is the most likely location of this inner 



Tributary divide. The sharp divide between the two deep 

 portions of the valley bottom has proven an evasive feature in the 

 later exploration. Two holes put down a short distance to the 

 southward (24/'A44 and 20 'A44) failed to find the rock floor so 

 high, one reaching rock at a depth of 181 feet and the other faihng 



