1012 THE GEOLOGY OP MINNESOTA. 



PLATE III. 



Page. 



FIGURE 1 Greenwacke, or pebbly tuff. Rock No. 1419, about \ 6 7i':; 



PIG. 2 Agglomerate, showing the devitrified glassy pulp which surrounds the 



large bombs. Eock No. 1510, about 2 T 5 733 



FIG. 3^Quartzyte, showing the rounded quartz grains surrounded by volcanic ash. 



Rock No. 1526, about 2 T 8 "37 



FIG. 4 Taconyte, showing the general oolitic structure and nuclei of volcanic glass 



broken before incorporation in the rock. Rock No. 1294, about \ 5 739 



FIG. 5 Taconitic iron ore, pisolitic. Rock No. 1294 739 



[This photo was actually made from rock No. 2135, about 2 j 5 .] 



FIG. 6 Taconyte, showing an amorphous globule which had been broken and again 



surrounded by concentric bands. Rock No. 1294, about -\ 6 739 



FIG. 7 Taconyte, showing nonconformity of the nuclei with the encircling bands. 



Rock No. 1294, about V 739 



FIG. 8 Taconyte, showing the general aspect in rock No. 1530, about s f 739 



FIG. 9 Taconyte, showing a compound nucleus of a taconitic grain, there being 

 eleven main parts; three of them of angular earlier quartz and the rest of 

 flint or devitrified glass. Rock No. 1530, about \ 739 



FIG. 10 Taconyte, showing broken encircling bands about a taconitic pebble, indi- 

 cating that the bands were earlier than the rock mass in which the pebble 

 lies. Rock No. 1530, about 2 T 6 739 



FIG. 11 Taconyte, showing the general aspect in rock No. 1630, about '-/ 751 



FIG. 12 Magnetitic iron ore in gabbro. Rock No. 1711, about 2 T 5 766 



