Page:VCH Warwickshire 1.djvu/32



the character of the dominant faunas and floras ; whole groups of animals and plants once abundant in our district now occupy a very subordinate position or are even extinct in Britain, and indeed in many cases have entirely ceased to exist.

We arrive then at this important principle—that different strata are characterized by fossils peculiar to each ; and in accordance with this rule the stratified rocks of the earth-crust have been classified into some ten or twelve distinct divisions or systems, each marked by a peculiar assemblage of fossils by means of which far-distant exposures of rocks of the same system can be identified. The great divisions are still further divided into groups and stages, the smallest of which are however of purely local value.

The rocks of Warwickshire belong some to the oldest, some to the newest of these systems ; but there are great gaps in the series—the rocks elsewhere present either were not deposited in our area, or, if laid down, were afterwards wholly removed.

The table on page 3 shows in descending order the various systems of rocks represented in Warwickshire.

An examination of the geological map will show that these rocks are by no means equally important so far as the constitution of the surface of our county is concerned ; in this respect the red rocks of the Trias have the pre-eminence. These occupy the greater part of the surface, while the succeeding Jurassic beds form a smaller fringe on the south and south-east borders. Projecting through an extensive aperture in the red Triassic coverlet are the so-called Permians and the Coal Measures of the Warwickshire coalfield, while from below the latter emerge the Cambrian and still older Archaean rocks of Nuneaton.

Irregularly spread over the uneven surface formed by the edges or outcrops of all these ' solid ' rocks are the superficial Pleistocene deposits, while the most recent of all are the still-forming alluvial tracts bordering the present rivers.

The surface-relief of the district is nowhere very bold ; the county forms part of an undulating plain bordered along its south-eastern and southern sides by the higher ridges and plateaux near Daventry, Edge Hill, and Chipping Norton. This same elevated tract circles round the Vale of Moreton and at Chipping Campden merges into the northern Cotteswolds ; it is formed by the tattered edge of the great sheet of Jurassic deposits which occupies much of the adjacent country to the south-east. That this edge or escarpment is gradually retreating in that direction is shown by its having left several isolated patches or ' outliers ' some miles in its rear, as for instance at Ebrington Hill, at Brailes, and at Knowle.

These Jurassic limestones and sandstones overlook the less elevated grounds of the Lower Lias and Trias, not only because they were superposed on them originally, but also by reason of their own greater durability, not being so easily washed away by rain and streams. Indeed it may be laid down as an axiom that the harder rocks will be 2