l8 NEW YORK STATE MUSEUM 



special means must be devised. If a trestle be proposed, one finds 

 that it would have to be 4>^ miles long (24,000 feet), and in some 

 places 300 feet high, and at all points large enough and strong 

 enough to carry a stream of water capable of delivering 500,000,000 

 gallons daily — a stream that if confined in a tube of cylindrical 

 form would have a diameter of about 15 feet. 



A steel tube might be laid to carry the water across and deliver 

 it again at flowing grade, but here one is met with the fact that it 

 would require a tube of unprecedented size and strength and if 

 divided into a number of smaller ones the cost would be greater than 

 that of a tunnel in solid rock. 



The other alternative is to make a tunnel deep enough in bed 

 rock to lie beneath surface weaknesses and superficial gorges and 

 in it carry the water under pressure to the opposite side of the 

 valley. This is the plan that seems best suited to the magnitude 

 of the undertaking and would seem to promise most permanent con- 

 struction. But no sooner is this conclusion reached than it is 

 realized that there are now several hitherto unregarded features 

 that assume immediate and controlling importance. Some of these, 

 for example, are (i) the possibility of old stream gorges that are 

 buried beneath the soil, (2) the position of these old channels and 

 their depth, (3) the kinds of rock in the valley, (4) their character 

 for construction and permanence, (5) the possible interference of 

 underground water circulation, (6) the possible excessive losses of 

 water through porosity of strata, (7) the proper depth at which the 

 tunnel should be placed, (8) the kinds of strata, and their respective 

 amounts that will be cut at the chosen depth, (9) the position arid 

 character of the weak spots with an estimate of their influence on 

 the practicability of the tunnel proposition. Then after these have 

 all been considered the whole situation must be interpreted -and 

 translated into such practical engineering terms as whether or not 

 the tunnel method is practicable, and at what point and at what 

 depth it should cross the valley, and at what points still further 

 exploration would add data of value in correcting estimates and 

 governing construction and controlling contracts. 



This is a general view of one case, the first one of any large 

 proportions in following down the aqueduct. There are many 

 others. In nearly all of them the importance of geologic. questions 

 is prominent. Many of them, of course, are of the simplest soft,- 

 but, on the other hand, some are among the most obscure and 

 evasive problems of the science. And they do not becotiae-any 



