226 NEW YORK STATE MUSEUM 



Line I 



Feet 



8 400 Yonkers gneiss — good quality 

 23 800 Fordham gneiss — good quality — to Harlem river 



1 000 Crossing Harlem river — probably fault zone in gneiss 

 4400 Fordham gneiss — good rock — to 135th street 



4 600 Inwood limestone — probably fair — 2d grade 



2 000 Inwood limestone — probably poor quality — 3d grade 

 I 000 Manhattan schist — good quality 



At this point the line unites with line F. Total length of line, 

 83,800 feet. 



A tabulation of these figures indicating estimated extent of rock 

 types is given below : 



LINE F LINE G LINE H LINE I 



Feet Feet Feet Feel 



Total length of line 85 600 87 000 85 600 83 800 



Length in Yonkers gneiss 7 600 8 400 8 400 8 400 



Length in Fordham gneiss 17 000 17 600 25 600 29 200 



Length in Inwood limestone and marginal 



contacts 3 600 3 600 3 400 6 600 



Length in Manhattan schist 51400 51400 42200 33600 



Comparative siimmary of types of formation (Comparative dis- 

 tances are expressed in percentages) 



ABC F G H I 



Yonkers gneiss 7-^ 9-4 7-Z 8.8 9.6 9.8 10. 



Fordham gneiss 8.1 15.3 26.3 19.8 20.2 29.9 34.8 



Contact zones 51 0.0 



8.3| 



4.2 4.1 3.9 7 



Inwood limestone i3-9 25.3 i5-2j 



Manhattan schist 58.5 42.6 7.8 60.0 59.0 49.3 40.1 



Ravenswood grano-dioritei 0.0 0.0 12.0 0.0 0.0 0.0 0.0 



Too little known to classify! 7.0 7.0 22.6 7.0 6.9 7.0 7.1 



1 The Ravenswood granodiorite has been proven by later explorations to 

 extend into the territory here marked as too little known to classify. 



As a group it is especially noticeable that the new lines F, G, H, 

 I, have a very much lower percentage of contact zones and lime- 

 stone. The percentages of gneisses have been notably increased, 

 and the unknown and questionable formations have been reduced 

 to approximately the lowest terms. 



