54 
THE GEOLOGIST. 
siderable alteration in stone containing much iron, under which 
circumstance it is generally reduced from a hardjstate to a soft 
and crumbling substance ; if the component parts of a stone be 
siliceous, with a calcareous cement, there is good reason to believe 
that such a substance will stand the weather tolerably well, for 
it may be considered the natural product, of which human inge- 
nuity has, from a very remote period, successfully formed an 
imitation in the commonest of all building materials, mortar. 
A defect to which all sandstones are liable is, that a portion of 
uncrystallized, carbonaceous, ochreous or earthy powder, some- 
times nearly fills the interstices between the crystals, forming 
occasionally what are called " clay balls,^^ and often lying be- 
tween the laminations. These are always injurious to the dura- 
bility of a stone, especially if they amount to any considerable 
quantity. 
It may be remarked with respect to sandstones generally that 
there is seldom any difference between the numerous beds, as 
regards their qualities of withstanding weather ; this is instanced 
in the Duke of Devonshire's quarries on the river Derwent, in 
those near Leeds, Huddersfield, Dundee, Edinburgh and Glas- 
gow, in some of these cases being a range of two hundred 
feet. 
The greatest objection to sandstones in an economic point of 
view, is the difficulty with which they are applicable to decora- 
tive purposes, and the expense of sawing. 
The C7^aigleith stone j which deserves to be classed amongst the 
best of sandstones, costs nearly four times as much to saw as 
Portland stone. 
It is important in many respects whether the component parts 
of sandstone be fine or coarse. Some kinds are composed of 
such large particles, as to be distinctly visible to the naked eye 
at several feet distance. The coarsest of Bramley Fall, and of 
other mill-stone grits from the vicinity of Leeds, are examples of 
this description : others are, on the contrary, so finely grained 
