NOEMAL SEDIMENTARIES OF HEMLOCK FORMATION. l53 



with the pyroclastics, the conglomerate shows nothing different from the 

 volcanic conglomerate already described. It is a transition rock between 

 the tuffs and the normal sedimentaries. 



Similai'ly, in sec. 34, T. 45 N., R. 33 W., a gradation occm-s in the 

 upper horizon of the Hemlock formation from the volcanic conglomerates 

 to the true normal sediments. The sediments are slates about 175 feet 

 thick, containing lenticular masses of limestone. These beds dip 80° to the 

 west, generally strike north, but vary in places a few degrees to the west. 

 They are underlain by conglomerates containing well-rounded volcanic 

 pebbles. This volcanic conglomerate grades from the coarse conglomerate 

 up into what might be termed a water-deposited volcanic sand. The peb- 

 bles are all of volcanic material. Between the conglomerates and slates is 

 a small area without outcrop. Overlying- the slates is a succession of tuffs 

 and lava flows. 



The slates in color range from light gray and green to purplish red, 

 and the lenses of limestone vary from cream color to purplish red. In thin 

 section the slates are seen to be composed of a felt of sericite, chlorite, and 

 qiiartz, with associated innumerable minute rutile cr3'stals, and 'here and 

 there a large spot of limpid quartz. A ferruginous carbonate is present in 

 all of them in porphyritic rhombs. Where chlorite i.s abundant, the slates 

 are a light green. Where iron oxide is abundant and the chlorite less plenti- 

 ful, the slates are purplish. 



The lenses of limestone are rather pure, consisting mainly of calcite, 

 with some few scattered areas of cherty silica. On the edges of the lenses 

 some of the slate material is found forming bands in the carbonate. These 

 intermediate phases grade on the one hand into the pure carbonate, and on 

 the other hand into the slate beds. From the crust of limonite, which may 

 be seen on the weathered surface of the rock, the calcite is evidently rather 

 ferruginous. The process of alteration is clearly seen under the micro- 

 scope, where many of the grains are surrounded by rims of hydrated oxide 

 of iron and hematite. 



ECONOMIC PRODUCTS. 



BUILDING AMD ORNAMENTAL STONES. 



The rocks of the Hemlock formation are not likeh' to be much used 

 for building purposes. The compact basalts possess in a high degree the 



