144 TOE CRYSTAL FALLS IKON-BEARING DISTRICT. 



and ill chains of crystals forming- dendritic growths. The oxide is clearly 

 secondary in these altered rocks. Since it also occurs secondarily in the 

 cement, it appears highly probable that it is an infiltration product formed 

 during or after the metasomatic process. 



In these conglomerates feldspar fragments are far more common than 

 they are in the tufis, and they show a well-defined, round, waterworn charac- 

 ter. (Fig. A, PI. XXXIII.) Likewise masses of in-alite are commonly 

 associated with the rounded feldspar. The uralite is taken to be altered 

 pyroxene fragments, though no proof of this beyond its association could be 

 offered, as the fragments show no characteristic pyroxene outlines. The 

 well-rounded nature of the volcanic pebbles makes it certain that they 

 have been deposited through the mediation of water and enables one easily 

 to distinguish the typical examples in the field. 



In size the fragments differ from one another just as they do in the 

 case of the eolian deposits (fig. B, PI. XXXIII). Many of the largest 

 are several feet in diameter, but more commonly they vary from a couple 

 of feet in diameter to small pebbles. Partly filling the interspaces and 

 aiding in cementing the larger fragments, with which they are associated, 

 are very fine grained fragments derived from the trituration of the water- 

 worn lapilli and blocks. The coarse bowlder conglomerates grade through 

 finer conglomerates into very fine material. This fine material shows beau- 

 tifully marked false bedding. (Fig. G, PL XXVII.) 



In one of the finer-grained rocks, in addition to the usual sedimentary 

 banding, there are bands which appear to have been caused by a further 

 sorting of the materials, some of these bands being composed almost exclu- 

 sively of uralite. They consequently represent bands which were originally 

 composed mainly of pyroxene fragments. In this case, when the fine ejecta- 

 menta settled through the water they were separated according to size of 

 grain and specific gravity, as in ore-dressing processes. 



Under the microscope other points of difference in addition to those 

 above mentioned are noted between the conglomerates and the tuffs or 

 eolian deposits. The fine-grained rocks corresponding nearly to the vol- 

 canic sand, do not consist of distinguishable rock fragments, but of clearly 

 rounded feldspar grains which have been enlarged by peripheral additions 

 of feldspar substance, bunches of uralite, some chlorite, and of spheiie 

 secondary after titanic iron. The photomicrograph. Fig. A, PL XXXIII, 



