CHAPTER VIII 

 ANCIENT MOODNA VALLEY 



Moodna creek enters the Hudson from the west between Corn- 

 wall and Newburgh not more than a mile north of the entrance 

 to the Highlands. It is a retrograde stream in its backward flow 

 similar to the Wallkill. But its channel at present is almost 

 wholly on glacial drift which it has trenched to a depth of more 

 than loo feet below the average adjacent surface. How much 

 of its retrograde course therefore may be postglacial is not so 

 clear. It seems necessary, however, to account for all drainage 

 on the north margin of the Highlands by streams flowing to the 

 Hudson northward. There is no notch low enough for their escape 

 elsewhere. The ancient Moodna must have carried most of this 

 run-off from the district occupying the angle between the Wall- 

 kill and the Highlands. This stream may have drained even more 

 of the region now forming the divide with the Wallkill than does 

 the present Moodna. In any case it must have been a stream of 

 considerable size, capable of excavating a valley or gorge of 

 greater prominence during the period of early Pleistocene rejuvena- 

 tion than now appears. Furthermore its position makes it highly 

 probable that tributaries of fair size entering in its lower course 

 were also effective enough to require consideration. This conclu- 

 sion has led to the exploration of the Moodna valley in consider- 

 able detail in preparation for the aqueduct work. 



The Catskill aqueduct is to cross the stream near Firth Cliffe, 

 which lies almost directly west of Cornwall-on-Hudson, and be- 

 cause of the low surface elevation across this valley, as in the 

 others, a pressure tunnel in rock is judged to be the most suitable 

 type of structure. The accompanying sketch map shows the 

 location. 



Explorations were conducted especially for the buried channels 

 and character of rock floor. 



Geologic features 



The region is one of chiefly Hudson River slate. But there 

 are inliers of the older rocks such as Snake hill which belongs to 

 a long ridge of Precambric gneiss and granite, brought to the sur- 

 face by folding and faulting and there are more rarely outliers of 

 younger formations such as Skunnemunk mountain. Farther north 



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