
SOILS AND SUBSOILS 373 
boulders and pebbles of the same kind, and multitudinous 
rounded stones of other types of rock, it eventually became 
sealed up in the great conglomerate that forms the base 
of the Old Red Sandstone system in Central Scotland. 
Ages pass away — Lake Caledonia vanishes, and _ its 
conglomerates, red sandstones, etc., and igneous .rocks, now 
forming part of a land-surface, are gradually denuded. The 
old conglomerate is largely broken up, and our liver-coloured 
quartz, again at liberty, becomes the sport of the waves upon 
a sea-beach of Carboniferous times. Reduced in size by 
constant attrition, but otherwise unchanged, it is eventually 
locked up in one of the numerous conglomerates of the 
period. What its history may have been throughout the 
vast zons which succeeded up to the close of Tertiary 
times, we cannot tell. Possibly it lay perdu during all that 
prolonged period in its Carboniferous bed. Or it may have 
been dug out at some distant date, and again played its part 
as a rolling-stone on sea-beach or river-floor. Eventually, 
however, it was enclosed in the bottom-moraine or boulder- 
clay of the great mer de glace that formerly overwhelmed all 
Scotland. In due time this mer de glace vanished, leaving 
its accumulations to be attacked and disintegrated in their 
turn. Nowadays, the boulder-clay is being eaten into by the 
sea, and our liver-quartz, once more set free, repeats its coastal 
wanderings, and for all that we can tell may yet survive to 
run through a similar cycle of changes again and yet again. 
But quartz is an exceptional mineral, in comparison with 
which the great majority of rock-formers are ephemeral. 
Few of the numerous complex silicates with which it is 
associated in crystalline igneous and metamorphic rocks 
survive the process of disaggregation by which these gradu- 
ally become broken up. Now and again the felspars, and 
even some of their ferromagnesian associates—all in a more 
or less altered state-—-may yet retain their individuality, and 
enter sparingly or more abundantly, as the case may be, into 
the composition of derivative rocks. In the case of arkose, 
for example, we have a rock derived immediately from the 
disaggregation of a granite, and consisting, therefore, of 
quartz, felspar, and mica, assorted and arranged by water 
action, The quartz may be more of less water-worn, and the 
