338 STRATIGRAPHICAL GEOLOGY. 



have not stated. The vacant space in Fig. 44, between 2 and 3, is on the 

 line of strike of a Hmestone containing Helderberg crinoids. Therefore 

 the rocks associated with it are to be regarded as of the same age. The 

 readier decomposition of the Hmestone has left the space vacant on the 

 section, being covered by a thick deposit of gravel. It is now an unan- 

 swered question whether these conglomerates are to be ranked with the 

 adjacent fossiliferous limestones, or with the coarser conglomerates asso- 

 ciated with the Cambrian slates. In the absence of definite knowledge, I 

 shall consider these conglomerates at North Lisbon as Helderberg, and 

 the other as probably Cambrian. It must not be forgotten that there are 

 sandstones and fine-grained conglomerates on the west side of the Blue- 

 berry Hill range readily referable to the Helderberg. Such are those on 

 Fitch hill, near C. Hastings's, Littleton, and numerous loose blocks scat- 

 tered along the unfrequented road back of Bald hill in the north-west 

 corner of Lisbon, 



I have a little further information about the Helderberg limestones 

 below North Lisbon, At D. Richardson's house, and in the river bank 

 adjacent, are several ledges of white limestone, some of them quite pure 

 carbonate of lime, standing nearly vertical. About one hundred rods be- 

 low, or nearly opposite J. Dexter's, 2d, the limestone appears on the same 

 side of the river, holding fragments of the large crinoids characterizing 

 this formation, both at Littleton and Bernardston, Mass. The limestone 

 is here only twenty-five feet wide, traversed by veins of pyrites and quartz. 

 Bunches and large masses of hornblende are associated with it in such a 

 way as to suggest the possibiHty of their belonging to the underlying 

 floor, as the Helderberg limestones and accompanying mica schists have 

 been subjected to a violent pressure. Nearly opposite are similar slates 

 and limestones at the water's edge, dipping 75° N. 22° W, Lastly, there 

 are calcareous beds exposed a short distance above the turn of the car- 

 riage-road up Whipple brook, dipping 75° N, 42° W, All these ledges, 

 of unquestionable Helderberg age, may be embraced in an area of a mile 

 and a quarter in length, and having a thickness of strata rudely estimated 

 at five hundred feet. 



It is a matter of interest to know whether the Helderberg rocks could 

 not be traced continuously from Fitch hill south-westerly along the west- 

 ern border of the Cambrian in Lyman. We have on this line of expos- 



