{ yet made { Volcanic Rocks In the preceding table (p. 29) a representation of the various great subdivisions or 'systems' of the beds which are found in the British Islands is shown. The names of the great divisions are given on the left-hand side, in the centre the chief divisions of the rocks of each system are enumerated, and on the right-hand the general characters of the rocks of each system are given. Berkshire is now part of an island and is a long way from the sea, but there have been times when the arrangement of land and sea on the globe was very different from what it is now. Our district has during some periods been part of a continent, and in others it has been overflowed by the sea. These changes in the distribution of land and water were due to movements of the crust of the earth, and very largely to movements of compression from the sides, causing folding of the strata of which the crust of the earth is composed. After many and great changes, at a time geologically recent, but still long before the beginning of history in the usual sense of the word, the district now known as Berkshire rose above the sea for the last time. Since that date deposits of clay, sand, etc., have been formed in our area, and their formation is indeed still going on to some extent, but though these are true geological deposits they are of no great thickness, seldom as much as 20 feet. They are, however, at or near the surface of the ground, and consequently exercise considerable influence on the character of the country. We will, however, leave them out of account for the moment and consider the deposits formed before the district finally rose above the sea. These deposits are usually spoken of as forming the solid geology of the area, and the three divisions, into which as we have said Berkshire is divided, are characterised as follows:-- 1. In the northern part of the county, including the Vale of White Horse, the geological strata are older than the chalk formation. 2. In the central part of Berkshire the chalk formation is at or near the surface of the ground. 3. In the forest country of south and east Berkshire, the surface is formed of geological formations newer than the chalk, but the chalk is always to be found underground if one goes deep enough. If we look at a sectional plan of geological strata we shall see that none of the formations which come to the surface in our county are of any great antiquity, but somewhere deep down, say over a thousand feet below us, there is a platform of much older rocks, upon which those that come to the surface rest in an irregular manner. What these old rocks may be we do not know, but probably New Red Sandstone and possibly beds of coal may occur amongst them.