248 THE MAEQUETTE IRON-BEARING DISTRICT. 



The pure dolomites, where merely shattered, have been cemented by 

 finely crystalline cherty quartz, or by coarsely crystalline dolomite, or 

 by these two combined. The brecciated pliases show numerous in-egular 

 complex fragments of the granular dolomite. The angiilarities of these 

 dissevered fragments are frequently the reverse of the fragments adja- 

 cent, proving conclusively that they have l)een broken apart. In a more 

 advanced stage of tlie dynamic action the complex fragments of the gran- 

 ular dolomite have a subangular or roundish appearance, so that tlie rock 

 as looked at with a low power resembles a conglomerate. These dissev- 

 ered fragments are united by cherty quartz, by coarsely crystalline dolomite, 

 or by the two interlocking. In some cases this secondary cherty quartz 

 has impregnated the rock through and through, so that minute irregular 

 veins of chert or geodal areas of quartz are scattered through the dolo- 

 mite. In a still further stage of silicification but a small amount of granular 

 dolomite may be seen in the chert veins. As a result of further silicifica- 

 tion considerable belts of chert are found interlaminated with the bands 

 containing less chert. Frequently these belts have oval or abrupt ter- 

 minations. Oftentimes after a first dynamic action and silicification the 

 rocks have been brecciated again, and have again lieen cemented by infil- 

 trating silica. In this case we have a cherty dolomite or a chert-breccia, 

 with a cement of newer chert. It is generally possible to discriminate the 

 earlier and later chert by the slightly different crystalline characters which 

 it has, and also because the later chert is sometimes mingled witli oxide 

 of iron. 



The argillaceous and siliceous dolomites have been brecciated and 

 cemented in the same way as the purer dolomites. In this case we have 

 both fragmental quartz and secondary cherty quartz intermingled. The 

 original quartz grains uniformly show undulatory extinction or fracturing. 

 Frequently during the folding the grains of quartz and feldspar have been 

 broken out of their background and have fallen into the crevices. These 

 are surrounded by and embedded in secondary infiltrated cherty quartz 

 and dolomite. 



The slates and quartzites interstratified in the Kona dolomite are not 

 here described, as they are in all respects similar to the We we slates and 



