GEOLOGY OF THE NEW YORK CITY AQUEDUCT 245 



This is more strikingly true of the southerly extension of this low 

 ground southward along Morningside Park. A very deep and 

 prominent preglacial stream came down from the gap between 

 Morningside and Central Parks. 



It is not yet proven that the fault has really raised the Morning- 

 side block. At least if there is such displacement it is not of suf- 

 ficient amount to bring up a different formation at any point 

 yet examined! It would be possible for 'the limestone to be brought 

 up to the surface, but except for a few pieces of interbedded lime- 

 stone no evidence has been secured. The occurrence of this, how- 

 ever, is thought to indicate proximity to the limestone contact. 



General geologic conditions established. Fourteen borings 

 have been made for the special purpose of determining exact con- 

 ditions. On the data of these holes there are several features now 

 established beyond question that were originally given only as prob- 

 abilities. The most important of these may be enumerated as fol- 

 lows : 



1 A very deep cross valley is now proven between 123d and 

 I26tli streets, and its profile can be plotted. 



2 A part of this ground is badly broken, as if belonging to a 

 fault zone, but most of the floor thus far tested is not in had con- 

 dition, i. e. it is not very badly crushed or decayed. 



3 The drift cover in this cross valley is more than 200 feet deep 

 over a distance of more than two blocks on the proposed line ( from 

 123d street to Manhattan street). 



4 The limestone contact lies more than 300 feet east of the pro- 

 posed line at this Manhattanville cross valley. 



5 At 12 1 St street the limestone-schist contact stands very steep 

 and is probably slightly overturned. This is indicated by the data 

 of hole no. 33. 



6 The contact line approaches nearer to Morningside Park in 

 passing southward, touching the park behveen iioth and 113th 

 streets and the contact is probably not overturned in this southerly 

 extension. 



3 Morningside to Central Parks 



The contact between Inwood limestone and Manhattan schist 

 follows nearly parallel with the Alorningside Park boundary on 

 the east side, but, because of its form, actually touches the park 

 only at the southern end between iioth and 113th streets. At the 

 north end it lies off more than half a block to the east. The Man- 

 hattan schist forms an escarpment because of its more resistant 



