l6 NEW ^ORK STATE MUSEUM 



cate ready circulation with tendency to cave development at a depth 

 much below present action of this kind, and a])pcar to give addi- 

 tional support to the belief in former continental elevation of con- 

 siderable amount. In New York city exploratory borings have 

 shown that decayed rock occurs in zones or streaks to depths reach- 

 ing in rare instances to more than 500 feet. In the immediate 

 vicinity fairly sound rock may be found. A study of the distribu- 

 tion of these decayed portions leads to_ the conclusion that tliey 

 always follow structural weaknesses of the rock, either a contact, 

 or a fault, or a crust zone, and that the decay to such extreme depth 

 has been caused by a ready circulation of surface waters along 

 those lines at a time when the continent stood at an elevation more 

 favorable for such movements than the present. Incidentally their 

 frequent occurrence throws some light on the question of prevalence 

 of faulting within the New York city area. 



A fundamental problem of the geology of southeastern New 

 York has to do with the character and history of the basal gneiss, 

 or the l^^ordham gneiss series, and the relation of overlying beds to 

 it. The tunnels now in process of construction will penetrate some 

 of those portions seldom reached and will add materially to the 

 data bearing upon this question. Exploratory borings have already 

 given indisputable proof of the existence of many thin intcrbedded 

 limestone layers within the banded Fordham gneiss series proper. 

 Nearly all of those discovered in this way lie beneath a heavy cover 

 of drift and could not have been found except by drilling. This 

 relation of certain limestone beds has been pointed out in former 

 reports, l)ut until recently the abundance of these interbeds has not 

 been appreciated. Surface weathering tends to obscure them on 

 the outcrops and this accounts in part for the difficulty of finding 

 many satisfactory cases in field work. 



Further study of the rock floor of ^Fanhattan and I^)rooklyn 

 indicates that the heavy drift cover has materially altered the out- 

 lines of Manhattan island and has displaced some of its streams 

 and connecting channels. The East river, shifted out of its former 

 course by the drift, is one of these. A drift-filled valley through the 

 lower east side in southern Manhattan is more than 100 feet deeper 

 than the present East river channel. 



Doctor Berkey's investigations of the problems which have been 

 brought into the foreground by these various engineering operations 

 have been supplemented ])y the work of other geologists in the city 

 of New York upon problems of immediate local concern. To 



