204 THE PENOKEE IKON BEARING SERIES. 



which are as regular as any of the slaty iron carbonates of the first type of 

 rock, the specimens vary to those in which the thin section shows apjiar- 

 ently no proper lamination, although in hand specimen there is always 

 some evidence of stratification. In these laminated phases the chert may 

 be a background for the iron oxide or the reverse, depending upon which 

 is predominant. 



The chert in the ferruginous slates varies from finely crystalline to the 

 very fine spotty quartz mingled with amorphous silica, characteristic of the 

 first type of rock. When the quai-t,z is of the more coarsely crystalline 

 kind the sections are often cut by veins of silica. In these cases the sec- 

 ondary nature of a portion of the silica at least is indicated by the fact that 

 it does not always lie directly parallel to the lamination, but breaks across 

 the more feiTUginous bands in little veinlets, while various singular depar- 

 tures from the regularity of the lamination indicate the same thing. Usually 

 the quartz shows little or no indication of a concretionary or brecciated 

 nature. The iron oxide is generally of the brown sojnewhat hydrated 

 hematite. Occasionally the hematite is bright red, when the rock becomes 

 a jas})er. These jaspery portions are not iisuall)' in anj^ great thicknesses. 

 Sometimes the rocks are quite regularl)' laminated, but often the jaspery 

 parts are in the shape of noncontinuous fine laminae. Less frequently the 

 oxide of iron is in part magnetite. 



The iron oxide is present in irregular areas, and frequently is in suffi- 

 cient quantity to form continuous ramifying areas in which the chert is 

 l)uried. In a portion of the specimens little or no iron carbonate remains, or 

 the iron oxide, either hematite or hydroxide, may present itself as mere 

 stains in the carbonate, replacing the carbonates in Aarying degrees, until 

 finally an entire crystal or bunch of crystals of that mineral is changed to the 

 oxides. Rhombic crystal sections, composed of oxides of iron, are to be 

 found in nearly all of the sections. In quite a good many cases all of the 

 iron oxide of a section, or nearly all of it, will present itself in these rhombic 

 shapes. More often the rhoml)s will be perceptible only on the edges of the 

 iron oxide areas, the middle portions of these aggregates being too compact 

 to allow of their i-ecognition. 'I'he carbonate itself is found in more than 

 half of the sections examined, and in nearly all of the remainder its former 



