Page:VCH Buckinghamshire 1.djvu/51

Rh rock known as malmstone, and is nowhere more than 25 feet thick in the district. Among the few fossils recorded, Avicula gryphæides is noteworthy.

The Upper Greensand is exposed at Bledlow Cross, Horsendon, near the railway stations of Princes Risborough, Monks Risborough, and Kimble, near Aston Clinton and Buckland ; and it has been proved in a boring near Marsworth. It has thinned out at Ivinghoe, but reappears at Eddlesborough.

Owing to its limited extent it is locally of no great importance, although the soil is fertile. A certain amount of water is held in the formation, and springs are thrown out where the Gault clay appears beneath the gentle scarp of Upper Greensand.

The Chalk comes to the surface over a large area in Buckingham- shire and forms the main foundation of the southern part of the county.

There is a passage upwards from the glauconitic sands and marls of the Upper Greensand into the Chalk Marl which forms the lowest division of the Chalk. So gradual indeed is the passage that as Mr. Jukes-Browne remarks, ' one cannot say where the Greensand ends and the Chalk begins ' at Bushey Leys near Eddlesborough and in Aston Clinton Park.

The Chalk Marl consists of clayey and slightly sandy chalk, which gives rise to a somewhat tenacious soil, suitable for the growth of wheat and beans.

At the top of this division there is a band or two of sandy lime- stone which has been extensively quarried at Totternhoe in Bedfordshire. It hardens on exposure and has been much used as a building stone, being well adapted for inside work. Hence it is known as the Tot- ternhoe stone. It yields Ammonites varians and Inoceramus, and outcrops below the main scarp of the Chiltern Hills above Bledlow and Princes Risborough, below Wendover, and at Ivinghoe. Locally it is but 2 or 3 feet thick. A mass of hard grey and white chalk and a band of softer marly chalk occur above the Totternhoe Stone completing what is known as the Lower Chalk. The Middle Chalk commences with a band of hard yellowish nodular chalk, known as the Melbourn Rock from its occurrence at Melbourn in Cambridgeshire. It is from 8 to 10 feet thick, and has been observed at Chalkshire, two miles west of Wen- dover. Above we find a mass of white chalk with few flints, which stands up boldly in the Chiltern range and may be seen at White Cliff Cross (813 feet), Combe Hill (852 feet) and Haddington Hill, and in the fine escarpment above Ivinghoe (8 1 1 feet) and Eddlesborough. It extends along the valleys to Great Missenden and West Wycombe.

Another rocky band occurs at the base of the Upper Chalk. This is a hard jointed chalk known as the Chalk Rock ; it is from 1 to 8 feet