34 



WALLINGFOED CONGLOMERATE. 



above the conglomerate to be shortly described, on the west side of those ponds in that 

 town. The facts here shown have a bearing upon our conclusions. 



FIG. 11. 







Section east of Plymouth Ponds. Dip 55 



More than nine-tenths of the pebbles in the Wallingford conglomerate are gray, some- 

 what granular, but often more or less hyaline quartz. White feldspar nodules are not 

 uncommon. Quartz is sometimes disseminated through the feldspar, so as to form a sort 

 of graphic granite. A few pebbles of distinct gneiss have been noticed. But it is not un- 

 usual for the micaceous cement to exhibit folia of feldspar, becoming in fact veritable 

 gneiss ; and perhaps the gneiss pebbles may all have thus originated. The most striking 

 pebbles of feldspar, however, are seen in a finer variety of the rock, destitute of quartz 

 pebbles, but showing small, white, rounded masses of feldspar, rarely over half an inch in 

 diameter. We are of opinion that all the feldspar pebbles, as well as the narrow strips 

 of gneiss, are the result of metamorphism ; that is, the pebbles were changed in mineral 

 constitution, and the gneiss actually formed by metamorphic processes. But we shall recur 

 to this subject again in the sequel. 



Most of the pebbles are somewhat elongated in the direction of the strike on a horizontal surface, so as 

 to give them an egg-shaped appearance. But where joints or other fissures have exposed the edges of the 

 strata at right angles to the strike, the elongation, flattening and bending of the pebbles are much more 

 striking, as the following outlines (Fig. 12), made by c. H. H., will show. Yet even here a few pebbles 

 seem not to have been modified at all in form, two of which are shown on the drawing. They seem not 

 to have been plastic, as the others were. 



Fia. 12. 



Elongated Pebbles, Wallingford. 



