. Elements of geology, or, The ancient changes of the earth and its inhabitants as illustrated by geological monuments. Geology. 756 IRREGULARITIES IN FOLIATION. [Ch. XXXVI. From what I have myself seen in the Grampians, both in Forfar- shire and Perthshire, I have always concluded that MacCnlloch was correct in the opinion that gneiss and mica-schist may be considered as stratified rocks, and that certain beds of pure quartz, one or two feet thick, which run for miles in the strike of their foliation, as well as the intercalation of masses of limestone, and of chloritic, actinolitic, and horn
. Elements of geology, or, The ancient changes of the earth and its inhabitants as illustrated by geological monuments. Geology. 756 IRREGULARITIES IN FOLIATION. [Ch. XXXVI. From what I have myself seen in the Grampians, both in Forfar- shire and Perthshire, I have always concluded that MacCnlloch was correct in the opinion that gneiss and mica-schist may be considered as stratified rocks, and that certain beds of pure quartz, one or two feet thick, which run for miles in the strike of their foliation, as well as the intercalation of masses of limestone, and of chloritic, actinolitic, and hornblende schists, all indicate the planes of original stratification. At the same time, I fully admit that the alternate layers of quartz, or of mica and quartz, of felspar, or of mica and felspar, or of carbonate of lime, are more distinct, in certain metamorphic rocks, than the ingredients composing alternate layers in most sedimentary deposits, so that similar particles must be supposed to have exerted a molecular attraction for each other, and to have congregated together in layers more distinct in mineral composition than before they were crystal- lized. We have seen how much the original planes of stratification may be interfered with or even obliterated by concretionary action in deposits still retaining their fossils, as in the case of the magnesian limestone (see p. Si). Hence we must expect to be frequently baffled when we attempt to decide whether the foliation does or does not accord with that arrangement which gravitation, combined with cur- rent-action, imparted to a deposit from Avater. Moreover, when we look for stratification in crystalline rocks, we must be on our guard not to expect too much regularity. The occurrence of wedge-shaped masses, such as belong to coarse sand and pebbles—diagonal lami- nation (see p. 16)—ripple-marked—unconformable stratification (p. 16), the fantastic folds produced by lateral pressure—faults of various width—intrusive di
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Keywords: ., bookcentury1800, bookdecade1860, booksubjectgeology, bookyear1868
