214 NEW YORK STATE MUSEUM 



The Rondout Valiey limestones are affected along joint planes, but 

 the effect is almost wholly confined to a simple enlargement of these 

 crevices. In the Inwood an additional eft'ect is the weakening of 

 the sutures or bond between the individual granules resulting in a 

 tendency to weaken the whole mass as far as there is much pene- 

 tration of seeping water. It would have less tendency to produce 

 openings or caves, but greater tendency to produce a rock that 

 would crumble in the hand or that would gradually assume the con- 

 dition of a lime sand or a micaceous mud. 



As to the eff'ect of water from the aqueduct on fresh portions of 

 this rock, it is certain that the rock would be attacked wherever 

 exposed to direct action. Its method of attack is by solution, and 

 the rate of attack may safely be reckoned as not materially different 

 from that assumed or being established by experiment and experi- 

 ence on the Rondout V^alley types. 



In the final consideration of the difficulties at Bryn Mawr the 

 engineers have decided to abandon the tunnel plan. It is probable 

 therefore that no additional explorations of direct bearing on the 

 problems of this ground will be made. 



