89 
Geology of GHiltshive. 
By G. Pouterr Scropr, Esq., M.P. 
ie N attempting a popular sketch of the Geology of Wiltshire 
fe for the readers of this Magazine, it will scarcely be advisable 
1o assume that they are all acquainted with even the rudiments 
of the science. Those, therefore, who already possess this informa- 
tion will, I trust, excuse my commencing with a brief notice of the 
_ general series of Rock Formations, of which our county presents on 
its surface only a portion. 
The science of geology is known to have for its object an exami- 
nation of the materials which compose the solid surface of the 
earth, with the view to deduce from thence some notions of its 
history, that is to say, of the successive physical changes it has 
undergone. © 
In the course of their investigations geologists have discovered 
a very remarkable similarity (though by no means an identity) in 
these materials, throughout every known part of the globe; that is 
to say, they observe in almost every country a succession of the 
same, or nearly the same rocks, or beds of solid matter, composed 
of nearly the same minerals, and having nearly the same structure 
and disposition. 
These matters, however, are readily distinguishable by their 
principal characters into two primary classes, viz.:— 
1. The Icnxous, or Crystalline rocks, which appear to form the 
base and solid scaffolding of the whole crust of the globe, and to 
have been in many places forcibly thrust up from beneath (whence 
they are also called Hypogene) through that surface, in a more or 
less imperfectly liquid state, and at an extremely high temperature, 
by Volcanic, or as it is often called, ‘Plutonic’ agency. These 
comprehend the varieties of Granite and Porphyry, Gneiss and 
