GEOLOGY OF THE NEW YORK CITY AQUEDUCT 



227 



Estimated summary of quality 



Good rock, first grade 

 Fair " second " 

 Poor "' third " 

 Unknown! (Brooklyn) 



LINE F 



Feet 



LINE G 



Feet 



LINE H 



Feet 



LINE I 



Feet 



53400 



56800 



54600 



49600 



23400 



21 400 



22400 



25200 



2800 



2800 



2600 



3000 



6000 



6000 



6000 



6000 



85 600 87 000 85 600 83 800 



All of this rock is now known to be of good quality. 



In other words these new lines show : 



LINE F LINE G LINE H LINE I 



Per cent Per cent Per cent Per cent 



First grade rock 62.3 65.3 63.8 59.1 



Second " 27.3 24.6 26.1 30.0 



First and second grades together. 89.6 89.9 89.9 89.1 



Third grade rock 3.2 3.0 3.0 3.6 



"Unknown" ground ^ 7.0 6.9 7.0 7.1 



^ Results of recent boring explorations show that this ground is first 

 grade also. 



A comparison on this basis with the original lines A, B, C indi- 

 cates that these new lines F, G, H, I, make a better showing, 

 especially on first grade rock and that all show decided reduction in 

 the third grade ground. 



First grade rock 49. 



Second grade rock 35 



First and second 85 



Third grade rock 7 



Unknown ^ 7 



A 



B 



c 



F 



G 



H 



I 



•4 



40.0 



49.0 



62.3 



65.3 



63.8 



59.1 



•9 



41. 1 



16.7 



27-3 



24.6 



26.1 



30.0 



•3 



81.0 



65.7 



89.6 



89.9 



89.9 



89.1 



•7 



II. 8 



II. 6 



3.2 



3-0 



3-0 



3.6 



.0 



7.1 



22.7 



7.0 



6.9 



7.0 



7.1 



1 Now known to be first grade. 



On geological grounds, therefore, it is confidently believed that 

 any one of the new lines (F, G, H, I) would give decidedly better 

 results than any one of the original ones (A, B, C). The poor 

 and the questionable and the unknown ground can not be wholly 

 avoided by any possible Hne, no matter how roundabout. In these 

 lines, approximately as drawn, the objectionable points are reduced 

 to a minimum with almost no increase in total length of conduit. 

 The objectionable portions are also restricted in large part to the 

 8 



