470 C. H. HITCHCOCK: — AMMONOOSUC DISTRICT, NEW HAMPSHIRE 



On the east side of Blueberry mountain the line of limestone outcrop 

 can be traced, but less satisfactorily. One is represented in figure 4, 

 plate 42. Between this point and Mill brook the rock has not been 

 seen for a distance of 4 miles along the line of strike, in an unfavor- 

 able region for observation. At North Lisbon, away from the proper 

 line of outcrop, it is found plentifully, as will be described later. South 

 from Mill brook the limestone with crinoidal fragments has been ob- 

 served, with the accompanying black slates and auriferous conglomer- 

 ates, as indicated by figure 6, plate 42. These outcrops are connected 

 with the faulted block of argillitic schist, and in the very south corner 

 of Lyman, extending into Bath, are continuations of all these different 

 kinds of rocks. 



The limestone at North Lisbon is situated along a different line of 

 strike. Commencing near the railroad bridge below the station, it is 

 finely developed and extends down the Ammonoosuc river for about 2 

 miles. The rock is white and carries large crinoidal fragments. A dike 

 of diorite, number 3 of Phalen's determinations (see beyond), cuts this 

 ledge. Near the mouth of Walker brook are hornblendic layers, sug- 

 gestive of a metamorphic change sometimes observed in calcareous 

 material. The importance of this range may appear in the fact that 

 erosion has been deeper here than along any other of the calcareous 

 lines of outcrop. Sandstones or quartzites accompany this range. 



To the east there is a still stronger calcareous band. It starts near 

 the south branch of the Ammonoosuc, about a mile southeast of Streeter 

 pond, and follows a northeast and southwest road past the " central " 

 school-house of Lisbon nearly to Salmon Hole brook. It underlies an 

 equally important band of quartzite, both dipping toward the Ammo- 

 noosuc. 



This duplex calcareous and silicious range is of even greater thickness 

 in its last known development farther east, from the old iron furnace of 

 Franconia past Sugar Hill village into Landaff, where the limestone 

 disappears, but the silica connects with the Coos quartzite of my report, 

 a formation traceable through New Hampshire into Massachusetts. 

 Limestone of considerable thickness is associated with it in Haverhill, 

 Orford, Lyme, and Plainfield. Through Lisbon the limestone usually 

 dips easterly beneath the quartzite, though there is a synclinal at Bron- 

 son's quarry. 



Thus there are five parallel bands attended by sandstone, quartzite, 

 or conglomerate. Three of them carry fossils, including the one afford- 

 ing the characteristic middle Upper Silurian forms. It is reasonable, 

 therefore, to suppose that all of them are of approximately the same age. 



Figure 5, plate 42, is a section illustrating the positions of the two 



