GEOLOGY of the Great Oolite Limestone and the Cornbrash ; only very small tracts of them come within the county of Rutland. (4) The Cornbrash. — This exhibits more constant characters than any other member of the Great Oolite Series. Its usual appearance is that of an earthy and shelly limestone, somewhat ferruginous and very fossiliferous. When quarried under a covering of clay it is always of a blue colour and exceedingly hard, but where it has been exposed to the percolation of water from the surface it has a light brown colour and breaks up into small flat slabs, each of which is usually coated with a stalagmitic deposit. The rock, thus weathered and disintegrated is locally termed kale. Its thickness appears to be from 8 to 1 5 feet. Only a few small tracts of Cornbrash occur within the limits of the county, its main outcrop lying for the most part just outside the boundary of our area, but running within it by Belmesthorpe and Banthorpe. The largest tract is the outlier on Barrowden Hill, another occurs north of Clipsham and there are two small patches near Ryhall. Though fossils are abundant in the Cornbrash they consist chiefly of Echinoderms, Brachiopoda and bivalve mollusca ; Gasteropoda are rare and Cephalopoda are not very common. The most characteristic species are Ammonites macrocephalus^ Avicula echinata, Ostrea Jiabelloides, Pecten vagans, 'Terebratula intermedia^ Waldheimia lagenalis, Holectypus de- pressus and Nucleolites clunicularis. The rock appears to have been formed in a tranquil sea at the commencement of an epoch of great subsidence. Towards the border of the Fenland it passes beneath the great clay formation which is known as the Oxford Clay. THE GLACIAL DEPOSITS As mentioned on p. 2, these deposits belong to a much more re- cent period of geological history than do the Jurassic rocks on which they lie. Moreover they were not formed by the ordinary processes of deposition, but have been accumulated in a more irregular and tumul- tuous manner by the operation of ice in ponderous masses, though opinions differ as to the conditions under which the ice acted. Some think that the British Islands were raised to a high level above the sea, that an ice-sheet was gradually formed over their northern portions, and that Boulder-Clay is a terrestrial deposit left by the passage of this ice- sheet across the country ; others believe that the passage of the ice was assisted by a gradual submergence which enabled masses of ice coming from several directions to rise higher and higher over the land and to carry rock-debris from lower to higher levels. The manner in which the Glacial deposits occur proves that the main features of the country, the hills and escarpments, the great plains and some of the valleys, had been developed before the beginning of the Glacial period. The greater part of England had been dry land through- out the Oligocene, Miocene, and Pliocene periods, and its surface had been sculptured into hill and vale, plain and plateau. Over this surface the I 9 2
