490 H. Hicks—Pre-Cambrian Volcanos and Glaciers. 
in Paleozoic, and subsequent times, metamorphism on a small scale 
did take place in consequence of disturbances combined with severe 
volcanic action no one will doubt; but the evidence is not satisfac- 
tory, to say the least of it, that any of the great groups deposited 
since Pre-Cambrian times have been metamorphosed under such 
intense influences as were then prevalent, or even have suffered more 
than a partial change, and that usually only over very limited areas. 
Evidences showing that glacial phenomena prevailed in Pre- 
Cambrian times were pointed out by me in a paper in the GroLoGicaL 
Magazine in 1876, and there can, I think, be little doubt, that 
glaciers did even at that early period spread over some of the higher 
lands. 
The Pre-Cambrian continent was doubtless studded not only with 
voleanic mountains, but also with high ridges and plateaux in 
northern latitudes, and many portions of this old continent are now 
visible from the latitude of 30° to the arctic regions. 
It could scarcely be expected, however, that much evidence would 
still remain after the numerous changes that have taken place over 
most of the surface of this old land since it commenced to be depressed 
to receive the Cambrian sediments. Yet that there is some such 
evidence still in existence seems to me clear. The angular character 
of many of the masses in the Cambrian rocks which rest immedi- 
ately ou the old Jand in the Highlands of Scotland, was mentioned 
by me in the Grot. Mae. 1880 (pp. 108-109; 155-166 ; 222-226; 
266-271); and I there refer to the so-called conglomerates as more 
properly “breccias.” I also stated that the old floor on which they 
rest “remains much as it was when the overlying rocks were 
deposited upon it.” More recently Prof. Geikie! has called attention 
to the same rocks at the same place (Gaerloch), also to the con- 
dition of the old floor, and attributes, as I had previously done, in 
several areas, the appearances to the action of land ice. In Wales 
also the Cambrian conglomerates, where they rest on the old floor, 
contain very large angular masses, though I have never recognized 
blocks as large there as those in the angular breccia which is 
presumably of Cambrian age near Gaerloch. 
In the paper in the Grou. Mac. for 1876, p. 157, after referring to 
the physical features of the old Pre-Cambrian land, I stated that— 
“this condition of continents of great size in high latitudes, with 
elevated plateaux and high mountains, would lead us to believe that 
they were covered with ice and snow in their higher parts, and that 
the plains and valleys had therefore much loose material strewn 
over them. In the Cambrian rocks in Wales boulders of con- 
siderable size, sometimes a foot in diameter, are often found in 
the beds of conglomerate, and the frequent alternations of con- 
elomerates, grits, and sandstones, seem to prove that, at least in 
the earlier epochs, an abundance of loose material must have been 
near and ready at hand to be easily denuded off as each part became. 
submerged. Marine action on the hard metamorphic cliffs alone 
could scarcely have produced so much sediment. Moreover, the 
1 Nature, Aug. 26, 1880. 
