218 THE OLD RED SANDSTONE. 
lar fragment appearing in some parts of the mass for yards 
together. The debris of our harder rocks rolled for centuries 
in the beds of our more impetuous rivers, or tossed for ages 
along our more exposed and precipitous sea-shores could not 
present less equivocally the marks of violent and prolonged 
attrition than the pebbles of this bed. And yet it is surely 
dificult to conceive how the bottom of any sea should have 
been so violently and so equally agitated for so greatly ex- 
tended a space as that which intervenes between Mealforvony 
in Inverness-shire and Pomona in Orkney in one direction, and 
between Applecross and Trouphead in another —and for a 
period so prolonged, that the entire area should have come to 
be covered with astratum of rolled pebbles of almost every 
variety of ancient rock, fifteen stories’ height in thickness. 
The very variety of its contents shows that the period must 
have been prolonged. A sudden flood sweeps away with it 
the accumulated debris of a range of mountains; but to blend 
together, in equal mixture, the debris of many such ranges, 
as well as to grind down their roughnesses and angularities, 
and fill up the interstices with the sand and gravel produced 
in the process, must be a work of time. I have examined 
with much interest, in various localities, the fragments of 
ancient rock inclosed in this formation. Many of them are no 
longer to be found in situ, and the group is essentially dif- 
ferent from that presented by the more modern gravels. On 
the shores of the Frith of Cromarty, for instance, by far the 
most abundant pebbles are of a blue schistose gneiss: frag- 
ments of gray granite and white quartz are also common ; and 
the sea-shore at half ebb presents at a short distance the ap- 
pearance of a long belt of bluish gray, from the color of the 
prevailing stones which compose it. ‘The prevailing color of 
the conglomerate of the district, on the contrary, is a deep 
