42 KINDLE 



ion, being almost due northwest and southeast. The well marked 

 and highly inclined bedding planes and the absence of any very 

 prominent system of joints afford the factors which, without any 

 knowledge from observation, might be used to predict the probable 

 direction of any underground stream or cavern. It was not sur- 

 prising therefore, to find that the direction of the subterranean 

 channel as exposed by the " cave-ins" coincided with the strike of 

 the beds in its vicinity. Moreover, the sides of the limestone chan- 

 nel descended where they could be observed, at an angle and in a 

 direction similar to that of nearby outcrops of the limestone and 

 evidently conform rather closely to bedding planes. (PL V.) 



At the time of the writer's visit all of the limestone channel which 

 was exposed had a direction of N. 48 W. The close agreement 

 between the direction of the exposed channel and the strike of the 

 rocks, and the evident predominant influence of strike and dip on 

 underground drainage led the writer at the time of his visit to sug- 

 gest to the city engineer that in all probability any future "cave- 

 ins" would be on or very near the 48 line passing through the first 

 series of "cave-ins." This prediction seems to be verified by the 

 alignment of a test drill hole which failed to reach bedrock, in Lewis 

 street at the southwestern end of the earlier series of cavings, and 

 by the last of the "cave-ins." Both of these were reported to be 

 exactly on the 48 line by the city engineer. 7 As already stated 

 the crevice thus located in Lewis street was uncovered by excavating 

 and arched with concrete across the width of the street in order to 

 forestall any possible further caving. Through the series of holes 

 caved in the marl and the drill records we have definite knowledge 

 of the position and direction of the subterranean channel for a dis- 

 tance of nearly 400 feet in a perfectly straight line (PL I). A large 

 number of test drillings has been made on both sides of this line 

 by the city engineer and the post-office authorities. All of these 

 have struck bed rock between 20 and 50 feet below the surface 

 except as noted above. These records, together with the fact that 

 the exposed portions of the limestone crevice into which the clay 

 and marl beds have slumped have in no case been outside the 48 

 line, seem to demonstrate that the course of the underground 



7 Letter of Aug. 31, 1910. 



