90 Geology of Wiltshire. 
Mica-schist, Trachyte and Basalt, or what are often called the Trap 
rocks, volcanic lavas, &c. Of this class of rocks we have no example 
in our county. 
2. The Aqueous or Stratified and Fossiliferous rocks, which are 
usually found above, or leaning against, the former class, often 
broken through, tilted up and bent, or even squeezed into folds, by 
the eruption, or subterranean expansion of these, and which are 
disposed evidently by the agency of water in strata (or beds), and 
generally (as their name implies) contain fossi/s, that is, the remains 
of organized beings, vegetable or animal. These Stratified (or as 
they are sometimes called Sedimentary) rocks, consist of slates, 
shales, puddingstones, sandstones, marbles, limestones, or clays, 
marls, sands, and gravels, of different qualities; for even these last, 
though loose in texture, are classed as rocks by geologists. Of these 
beds the hardest and most compact, generally speaking, lean 
against, or rest immediately upon, the erystalline rocks, and the 
looser and softer lie above them. Mountain ranges, for example, 
are usually found to be composed of a central axis, or back bone, 
of Hypogene crystalline rock, while the sides are formed of strata 
of slate, sandstone or limestone, lying one over the other and slo- 
ping, or as it is called, dipping away from the axis towards the 
plains below, which are formed of nearly horizontal beds of sand, 
clay, and gravel, such as the rivers or seas form in the present day 
out of the worn and ground-down fragments of the harder rocks. 
This, however, is only a general, not an universal rule, for the 
stratified rocks are occasionally found, as has been said already, 
carried up to very high levels, or tilted and set on end, or broken 
and twisted, evidently by some violent heavings or expansions of 
the crystalline matter below. And when this has happened, the 
strata above these are usually seen to lie across the broken or worn 
edges of the former, or ‘unconformably,’ as it is called, in contrast 
to the conformable or parallel disposition in which strata are 
usually found, and in which they were for the most part deposited. 
For (as I should perhaps have just said) all the stratified rocks 
are shewn by their composition to have been formed out of sand, 
clay, mud, or chalky matter deposited by water, either as drift or 
