FAULTS L-L, M-M AND D-D. 291 



are the main dislocations of tlie vicinity. Tliey differ from tlic remain- 

 ing faults of the region, so far as the evidence goes, merely in magnitude. 

 They are the main lines of displacement; the other faults are hut minor 

 breaks in tlie faulted l)locks into which the great l)reaks divide the region. 

 In this vicinity these great faults have a roughly north -and-south direc- 

 tion, but in the region as a whole there is no probability that this will 

 be found to be the case. 



FAULTS OF THE SECOND CLASS. 



Fault L-L. — Two sets of facts indicate a break along the line L-L. 

 First, the beds of middle Chazy age on both sides of the line have a much 

 greater width of surface outcrop than their thickness entitles them to at 

 the measured angle of dip ; second, tlie angle of dip is abruptly increased 

 along that line, otherwise being quite i)ersistent on either side. It is 

 probable that there is also repetition of a part of the series, but more 

 detailed work than has yet been possible is necessary in order to furnish 

 the proof. The fault is a strike-fault with downthrow to the south, and 

 a throw certiiinly less than the thickness of the middle Chazy — 25U feet, 

 and probably considerably less. 



Fault M-M. — North of L-L is another fault of the same character, bear- 

 ing to the northeast instead of the southeast, and with the thrown block 

 on the north instead of the south side. At the west end of the fiiult 

 Black River limestone is exposed on the thrown side ; beds of the middle 

 division of the Chazy on the heaved side. The missing strata are at least 

 200 feet thick, and the dip and strike on the opposite sides of the fault- 

 plane are (juite unlike. At the eastern end of the fault middle Chazy 

 beds on the south are brought up against Trenton on the north, the exact 

 horizon in the latter being unknown. The Trenton limestone along lake 

 Cham plain has not yet been carefully studied. That the throw of the 

 fault increases in amount from west to east is, however, clear from an 

 inspection of the dip and strike on the two sides. 



Fault D-D. — While it is uncertain whether this supposed fault belongs 

 to the second or third group, as herein classified, its descri})tion may })e 

 conveniently given now. 



The line of the fault is occupied l)y a wide marsh, so that an interval 

 of half a mile separates the first outcrui)S on one side from tliose on the 

 other. North of the marsh are ])eds of lower and middle Chazy age in 

 normal relations to one another and with a strike normal to the line of 

 tlie marsh. On the other liand, south of the marsh are found beds of 

 lower Chazy age alone, with different strike and dip. It should be stated 

 that in the triangular section of country enclosed between the faults A-A 

 and D-I) tlie relations are obscunj and not v(.'t fullv workc'd out. Out- 



