OF THE SANDSTONES. 35 
niogeneous paste of the same material, afford very fine examples. 
In some of these the pebbles are large, of fine texture, and exhi- 
bit a great variety of colour. These if cut and polished, which 
by reason of their great hardness would be a difficult operation, 
would be very beautiful. In others the grains are so small that 
the mass constitutes a kind of fine sandstone. In some the peb- 
bles make up almost the whole mass of the rock, in others they 
appear only here and there, thinly scattered through the basis in 
which they are imbedded. Conglomerates may be seen about 
Hillsborough, Pittsborough, Lawrenceville, in the western part 
of Randolph, and at some of the principal gold mines within the 
limits of the transition formation. 
Jl Breccia differs from a conglomerate in but one circumstance. 
The imbedded fragments, instead of being rounded by attrition, 
are angular. Both this and the conglomerates are siliceous, ar- 
gillaceous, or calcareous, according to the mineral character of 
the fragments and cement of which they are composed. Of n 
calcareous breccia the beautiful pillars of the capitol at Wash- 
ington may be cited as an example. 
OF THE SANDSTONES. 
21, The name of these rocks indicates what they are. In their 
composition, structure, and colour, there is a considerable variety. 
They consist chiefly of particles of siliceous sand, held together 
by a cement which is generally small in quantity, and sometimes 
apparently, by an attraction of aggregation exerted directly be- 
tween themselves. The sandstones are evidently of very differ- 
ent ages, but still bear such a resemblance to each other that 
they must be distinguished by their geological position, and rela- 
tions to other rocks, rather than their mineral characters. 
1. In the northwestern part of Scotland there is a sandstone 
which alternates with gneiss and quartz rock, and also with gray- 
wacke, and which must therefore be accounted one of the oldest 
members of the transition class. 
2. A stratum of sandstone., generally of a red colour, intervenes 
between the transition and secondary rocks in certain parts of 
England and Scotland, which is referred by some geologists to 
the former, and by others to the latter class. It is composed of 
particles of sand, generally with a mixture of mica, and sometimes 
of feldspar, or carbonate of lime, united by a cement of ferrugi- 
nous clay, which is seldom abundant. It is called the old-red- 
sandstone, but geologists seem inclined at present to regard it as 
a variety of gray-wacke. It underlies all the mines of fossil coal 
that have been discovered on the island of Great Britain. They 
are either imbedded in it, or what is more common, separated 
from it by one or two intervening strata, 
3. Another stratum of sandstone of more recent formation than 
the last, as is proved by the circumstance of its being above the 
