186 THE OLD RED SANDSTONE. 
The Old Red Sandstone of Scotland has been extensively 
employed for the purposes of the architect, and its limestones 
occasionally applied to those of the agriculturist. As might 
be anticipated in reference to a deposit so widely spread, the 
quality of both its sandstones and its lime is found to vary 
exceedingly in even the same beds when examined in differ- 
ent localities. Its inferior conglomerate, for instance, in the 
neighborhood of Cromarty, weathers so rapidly, that a fence 
built of stones furnished by it little more than half a century 
ago, has mouldered in some places into a mere grass-covered 
mound. The same bed in the neighborhood of Inverness is 
composed of a stone nearly as hard and quite as durable as 
granite, and which has been employed in paving the streets of 
the place —a purpose which it serves as well as any of the 
igneous or primary rocks could have done. At Redcastle, 
on the northern shore of the Frith of Beauly, the same con- 
glomerate assumes an intermediate character, and forms, 
though coarse, an excellent building stone, which, in some of 
the older ruins of the district, presents the marks of the tool 
as sharply indented as when under the hands of the work- 
man. Some of the sandstone beds of the system are strongly 
saliferous; and these, however coherent they may appear, 
never resist the weather until first divested of their salt. ‘The 
main ichthyolite bed on the northern shore of the Moray 
Frith is overlaid by a thick deposit of a finely-tinted yellow 
sandstone of this character, which, unlike most sandstones of 
a mouldering quality, resists the frosts and storms of winter, 
and wastes only when the weather becomes warm and dry. 
A few days of sunshine affect it more than whole months of 
high winds and showers. ‘The heat crystallizes at the surface 
the salt which it contains; the crystals, acting as wedges, 
throw off minute particles of the stone ; and thus, mechani- 
