GEOLOGY OF THE CONNECTICUT VALLEY DISTRICT, 323 



Our general impression of the age of this new series is, that it is alHed 

 to the Helderberg. The Coos group disappeared finally about two miles 

 below the Lisbon section, so that the Swift Water series lies contiguous 

 to gneiss of a very ancient period for five or six miles. Were the pres- 

 ence of chlorite an index to its age, it would be ranked with the Lisbon 

 group. No one need be troubled by the apparent dip both of the Coos 

 and Swift Water groups, as well as of the Helderberg strata beneath the 

 Lisbon series ; for the lateral force has been exerted so forcibly in New 

 Hampshire that inversion is the rule rather than the exception. 



Postscript. With the view of finally settling the relations of the Swift 

 Water series to the Huronian and adjacent rocks, I have reexamined the 

 Ammonoosuc valley between Lisbon and Littleton while the foregoing 

 pages were being set up, and think evidence is afforded to prove them to 

 be a part of the Huronian, perhaps the equivalent of the strata developed 

 along the Upper Ammonoosuc river in Stark and Milan (p. 52). This will 

 enable us to color the area between the clay slates and the Coos group 

 in Lisbon as Huronian. The Bethlehem group at North Lisbon may 

 extend a little farther south-west than appears on Fig. 27, and the small 

 area of it by M. Kimball's may be eliminated. I also think that the slate 

 band, spoken of as extending from Swift Water river past I. Clark's to 

 the north part of Lisbon village, should not cross the Ammonoosuc to 

 join the rock near Mrs. Bishop's, but continue to North Lisbon, perhaps 

 dividing above the saw-mill near the mouth of Whipple brook, and the 

 western branch continuing over Walker hill, constituting the whetstone 

 quarries there, and outcropping at Paddleford's just in the limits of Lit- 

 tleton. If there is to remain any relic of the Swift Water series in our 

 classification, it will be this band of slate. I cannot fully satisfy myself 

 whether it belongs to the Huronian, Coos, or Helderberg series. Future 

 explorers of this district may well commence by fixing the age of this 

 slate. A hornblende band lies adjacent to this slate on the west, trace- 

 able perhaps from Lisbon village, certainly from about the mouth of the 

 Salmon Hole brook to W. K. Chase's and the adjacent saw-mill, G. H. 

 Buel's, J. Clark's, and so on into Littleton at or near Fitch Hill summit. 

 I suppose the same, or a closely-related hornblende band, courses to 

 Streeter pond from the Whipple Brook saw-mill. This is the band spoken 

 of on page 284, and it is to be regarded as Huronian. 



