222 NEW ^'ORK STATE MUSEUM 



free from fault crushing and surficial weathering are the best 

 variety; that the more heavily buried areas of these rocks, together 

 with those limestone areas that are known to be the most substan- 

 tial of its class, should be regarded as fair or second grade ; that 

 the more obscure areas of limestone and all portions crossing 

 faults or rivers or crush zones in any rock must be regarded a^ 

 poor or third grade. This rating is based wholly on rock char- 

 acter and without any consideration of cost of construction. 



From the above it is clear that line A has more '' first grade " 

 rock than either B or C and less '' third grade " ground. 



Line C has three times as much '' unknown " ground as either 

 B or C and less " first '' and '' second grade " rock. 



In other words, the three lines are estimated : 



LINE A LINE B LINE C 



Per cent Per cent Per cent 



First grade rock 49-4 40 . o 49 • o 



Second grade rock 35 .9 41 , i 16. 7 



First and second grades together 85 . 3 81.0 65 . 7 



Third grade rock y .y 11. 8 11. 6 



Unknown ground 7.0 7.1 22. 7 



In addition to these differences of quality, it appears from a 

 study of the areal geology along the respective hues that a tunnel 

 wo'uld pass across limestone contacts from one formation to an- 

 other six times on line A, four times on line B, and seven times 

 on line C. These may all be considered points of probable 

 weakness. 



All of the lines cross belts of well known weakness believed to 

 represent fault zones. Line A crosses three such zones, line B 

 crosses two, and line C crosses at least three. 



Furthermore, all of the lines cut limestone for greater distances 

 than seems desirable or necessary. The weakest ground and the most 

 uncertain quahty of ground that can be mapped falls within the 

 limestone areas. In this respect line A with 13.9^ of limestone 

 ground is preferable to line B, with 25. 3^^ or line C, with 15.2^. 



From the above it is apparent that line C is least defensible. 

 Line A has some advantage over both of the others, especially in 

 quantity of first grade rock quantity of first and second grade 

 together, low amount of the known poorest grade and small extent 

 of the so called " unknown " ground. 



The chief advantage of line A over line B lies in its much 

 smaller limestone area (12,000 feet vs. 21,400 feet or 13.9;^ vs. 



