304 STRATIGRAPHICAL GEOLOGY. 



diameter, from ten to a hundred feet in width. Owing to its hardness it 

 has resisted disintegration better than the adjacent schists, and hence its 

 outcrops are usually very conspicuous. It is this feature which led me 

 to study its distribution with great care, so that it might be possible to 

 obtain a clue to the stratigraphical structure of the whole field. The 

 knowledge of the curves, breaks, and throws of this member illustrates 

 finely the difficulties in the way of elucidating completely the intricacies 

 of New Hampshire geology. The adjacent schists must be broken and 

 curved precisely like the conglomerate. Upon the map I have deline- 

 ated only the outcrops, without attempting to connect them together. 

 Doubtless in many cases there can be no direct connection, the forma- 

 tion having been broken into pieces which became widely separated from 

 one another. In other cases I have not yet been able to satisfy myself 

 how the connecting lines should be drawn. 



Besides quartz I find occasionally pebbles of jasper, chlorite, and both 

 the green and white schists. I do not recall examples of pebbles much 

 more than two inches in diameter. The cementing material is analogous 

 to the composition of the adjacent schistose rocks. There may be a few 

 cases of the distortion of the component pebbles by pressure, but they 

 are mostly roundish or elliptical. Metamorphism has operated upon this 

 conglomerate, so that the pebbles often seem to run into the cement by 

 imperceptible gradations; and a piece freshly broken from a few feet 

 depth does not readily display the fragmentary structure brought out 

 upon the surface by weathering. I have occasionally seen the pebbles 

 cut through by the jointed structure traversing the ledge. It is very 

 common to see small reticulated veins of quartz traversing these ledges, 

 especially in the neighborhood of a sharp bend or break in the continuity 

 of the formation. Indeed, so intimate is the connection between these 

 two phenomena, that, whenever I discover the numerous white veins, I 

 conclude immediately this must be in the vicinity of a bend, and never 

 fail to observe other tokens of its presence. In limestones the corre- 

 sponding feature is seen in the presence of similarly disposed veins of 

 white calcite. The designation auriferous came to be applied to this 

 rock by way of contrast with other fragmentary accumulations. Several 

 openings had been made in this member for the purpose of mining gold ; 

 and the mass has yielded from forty cents to two dollars per ton upon 



