GEOLOGY. 445 



ated rocks, and have, moreover, caused profound secular changes in the 

 constitution of the ocean's waters. The decay of sulphuretted ores in 

 the Eozoic rocks has given rise to oxidized iron ores, and also to de- 

 posits of rich copper ores at various geological horizons. 



5. That the rounded masses of crystalline rock left in the process of 

 decay constitute not only the bowlders of the drift, but, judging from 

 analogy, the similar masses in conglomerates of various ages, goiug 

 back to Eozoic time, and that not only the form of these detached 

 masses, but the outlines of eroded regions of crystalline rocks, were 

 determined by the preceding process of subaerial decay of these rocks. 



As regards the rocks of the Scottish Highlands noticed in the report 

 of last year, and especially of the so-called younger gneiss, Callaway has 

 continued his studies iu that region, and has considered its relation to 

 the Paleozoic series. This gneiss, the Grampian series of Hicks, is called 

 Caledonian by Callaway, and, as we have previously said, is apparently 

 identical with the series already named Montalban in North America, 

 and includes in its lower part, in Scotland, the granulites of Nicoll. 

 Some of its rocks have a certain resemblance to the older Hebridian 

 (Lewisian or Laurentian) gneiss, which is often porphyritic and has 

 been by some observers described as an igneous rock. 



The accompanying Paleozoic (Cambrian) strataare named by Callaway 

 the Assynt group, and consist at the base of what has been called the 

 Torridon sandstone, followed by a quartzite, sometimes with annelids, 

 flagstones or grits with Salterella, and a mass of dolomite. The Caledo- 

 nian gneiss appears in some cases to overlie directly this Assynt group, 

 this relation according to Callaway being due to a dislocation of the 

 strata, with a great thrust from the east which has squeezed together 

 both series of strata into a succession of folds overturned to the west, 

 giving to the whole series a general easterly dip. The Caledonian gneiss 

 is seen in Glen Coul to overlie immediately the Hebridian gneiss, while 

 elsewhere this same older gneiss is directly overlaid by the Cambrian 

 quartzite, which again is seen resting in outliers upon the younger gneiss. 

 This latter is penetrated by numerous granitic veins, which never pen- 

 etrate the Assynt group. Callaway notes between the Hebridian or Lau- 

 rentian gneisses on the west and the Caledonian on the east (the Assynt 

 group occupying the interval), several nearly parallel north and south 

 faults, which increase in upthrow from the west to the east. Thus the 

 first of these brings up the basal sandstone through the quartzite, then 

 faults more to the eastward bring up the sandstone through the over- 

 lying dolomite, and finally the underlying Hebridian gneiss itself; the 

 younger or Caledonian gneiss appearing in its proper place still farther 

 to the east. This is very similar to the successive faults long since ob- 

 served and described all along the western side of the Atlantic belt in 

 North America, the general structure of which is repeated in the Scot- 

 tish Highlands. Similar foldings have been pointed out by Brogger in 

 Scandinavia, where lower Paleozoic rocks are closely folded in the Eozoic. 



