762 HIGHLAND METAMORPHIC ROCKS. [Ch. XXXVn. 



gneiss between fossiliferous strata may, I conceive, be ascribed to 

 mechanical derangement. Almost any hypothesis of repeated changes 

 of position ma}^ be resorted to in a region of such extraordinary con- 

 fusion. The secondary strata having first become vertical, may then 

 m certain portions have become metamorphic (the plutonic influence 

 ascending from below), while intervening strata remained unchanged. 

 The whole series of beds may then again have been thrown into a 

 nearly horizontal position, giving rise to the superposition of crystalline 

 upon fossiliferous formations. 



It was remarked, in Chap. XXXIV., that as the hypogene rocks, 

 both stratified and unstratified, crystallize originally at a certain 

 depth beneath the surface, they must always, before they are upraised 

 and exposed at the surface, be of considerable antiquity, relatively to 

 a large portion of the fossiliferous and volcanic rocks. They may be 

 forming at all periods ; but before any of them can become visible, 

 they must be raised above the level of the sea, and some of the rocks 

 which previously concealed them must have been removed by denuda- 

 tion. 



In Canada, as we have seen (p. 583), the Lower Laurentian gneiss, 

 quartzite, and limestone, may be regarded as metamorphic, because 

 organic remains (Eozoon Canadense) have been detected in a part of 

 one of the calcareous masses. Nor can we doubt that the Upper 

 Laurentian, or Labrador series, consisting of gneiss, with Labrador- 

 felspar and felstones, in all 10,000 feet thick, have assumed their 

 crystalline structure by metamorphic action, since they lie in uncon- 

 formable stratification on the Lower Laurentian. The remote date of 

 the period when some of these old Laurentian strata of Canada were 

 converted into gneiss, may be inferred from the fact that pebbles of 

 that rock are found in the overlying Huronian formation, which is of 

 Lower Cambrian age, if not older (p. 583). The oldest stratified 

 rock of Scotland is the hornblendic gneiss of Lewis, in the Hebrides, 

 and that of the northwest coast of Rossshire, represented at Ahe base 

 of the section given at p. 67, fig. 90. It is the same as that inter- 

 sected by numerous granite veins, which forms the cliffs of Cape 

 Wrath, in Sutherlandshire (see fig. 743, p. 712), and is conjectured 

 to be of Laurentian age. Above it, as shown in MacCulloch's section 

 (fig. 90, p. 67), lie unconformable beds of a reddish or purplish sand- 

 stone and conglomerate, nearly horizontal, and between 2000 and 

 3000 feet thick. In these ancient grits no fossils have been found, 

 but they are supposed to be of Lower Cambrian date, and they cer- 

 tainly do not belong to the Old Red, as was formerly supposed, for 

 they have been shown by Sir Roderick Murchison to pass in the 

 North Highlands or in the three northern counties of Scotland, under 

 quartz rocks, which, with a subordinate limestone, rest unconformably 

 upon them. In this limestone, in 1854, Mr. Charles Peach found 

 some obscure organic remains, which led Sir R. Murchison to insti- 

 tute a searching inquiry, and eventually to establish beyond all doubt 



