224 NEW YORK STATE MUSEUM 



The question of shifting the Hnes is a compHcated one and hinges 

 more upon rock conditions, durabihtv, and location of weak zones, 

 than on any possible cost. 



Advisable changes in lines 



Xone of the suggested lines are defensible from a geologic point 

 of view for the reason that a much better one may be obtained by 

 no very serious shifting. 



In the general consideration of relative advantages of different 

 possible locations of the line, it is believed that the following large 

 features are of most immediate importance: 



1 The ridges as opposed to the valleys. 



2 The hard fonxiations as opposed to the softer ones. 



3 The crossing of few contacts as opposed to crossing many. 



4 The location well within a formation as opposed to location 

 along a contact zone. 



It is distinctly preferable from a geologic standpoint (i) to fol- 

 low the ridges, (2) to keep in the hard formations, (3) to avoid 

 many changes from one formation to another, (4) to keep away 

 from contact zones, and (5) to avoid weak zones, if possible, or 

 cross known troublesome zones at the most advantageous point. 



Recommendations of new lines F, G, H, I 

 The original lines A, B and C are marked on the map in blue 

 [pi. 32]. In addition several trial lines are sketched in yellow, any 

 one of which would give better geological conditions than any of 

 the three original lines. The newly suggested trial lines diiler from 

 each other chiefly in the points at which they cross the limestone 

 belts and weak zones. In all of them the central idea has been to 

 follow the gneiss and schist ridges as persistently as possible. All 

 unite at Central Park and are intended to follow Fifth avenue, 

 Broadway, the Bowery and ^vlarket street to East river along one of 

 the original lines. Xorth of Central Park they differ from the orig- 

 inal lines. The westerly one crosses the Harlem river at 176th 

 street and may be designated line F. The easterly line may also cross 

 the Harlem river at 176th street and may be designated line G; or 

 it may continue southward and cross the Harlem at 155th street. 

 It will then join the first one in the vicinity of 144th street and is 

 called line H. The alternative easterly one which crosses the Har- 

 lem at 155th street and follows Seventh avenue to Central Park is 

 line I. 



