Buckinghamshire (abbreviated Bucks) a south midland county of England, bounded N. by Northamptonshire, E. by Bedfordshire, Hertfordshire and Middlesex, S. for a short distance by Surrey, and by Berkshire, and W. by Oxfordshire. Its area is 743.2 sq. m. The county is divided between the basins of the rivers Ouse and Thames. The first in its uppermost course forms part of the north-western boundary, passes the towns of Buckingham, Stony Stratford, Wolverton, Newport Pagnell and Olney, and before quitting the county forms a short stretch of the north-eastern boundary. The principal tributary it receives within the county is the Ouzel. The Thames forms the entire southern boundary; and of its tributaries Buckinghamshire includes the upper part of the Thames. To the north-west of Buckingham, and both east and west of the Ouzel, the land rises in gentle undulations to a height of nearly 500 ft., and north of the Thames valley a few nearly isolated hills stand boldly, such as Brill Hill and Muswell Hill, each over 600 ft., but the hilliest part of the county is the south, which is occupied by part of the Chiltern system, the general direction of which is from south-west to north-east. The crest-line of these hills crosses the county at its narrowest point, along a line, above the towns of Prince's Risborough and Wendover, not exceeding 11 m. in length.
This line divides the county into two parts of quite different physical character; for to the south almost the whole land is hilly (the longer slope of the Chiltern system lying in this direction), well wooded, and pleasantly diversified with narrow vales. The chief of these are watered by the Wye, Misbourne and Chess streams. The beech tree is predominant in the woods, in so much that William Camden, writing c. 1585, supposed the county to take name from this feature (A.S. boc, beech). In the south a remnant of ancient forest is preserved as public ground under the name of Burnham Beeches. The Chilterns reach a height of nearly 900 ft. within the county.
The northern half of the county is occupied by Jurassic strata, in the southern half Cretaceous rocks predominate except in the south-eastern corner, where they are covered by Tertiary beds. Thus the oldest rocks are in the north, succeeded continuously by younger strata to the south; the general dip of all the rocks is south-easterly. A few patches of Upper Lias Clay appear near the northern boundary near Grafton Regis and Castle Thorpe, and again in the valley of the Ouse near Stoke Goldington and Weston Underwood. The Oolitic series is represented by the Great Oolite, with limestones in the upper part, much quarried for building stones at Westbury, Thornborough, Brock, Whittlewood Forest, etc.; the lower portions are more argillaceous. The Forest Marble is seen about Thornton as a thin bed of clay with an oyster-bearing limestone at the base. Next above is the Cornbrash, a series of rubbly and occasionally hard limestones and thin clays. The outcrop runs by Tingwick, Buckingham, Berehampton and Newport Pagnell, it is quarried at Wolverton and elsewhere for road metal.
Inliers of these rocks occur at Marsh Gibbon and Stan Hill. The Oxford Clay and Kimmeridge Clay, with the Gault, lie in the vale of Aylesbury. The clay is covered by numerous outliers of Portland, Purbeck and Lower Greensand beds. The Portland beds are sandy below, calcareous above; the outcrop follows the normal direction in the county, from south-west to north-east, from Thame through Aylesbury; they are quarried at several places for building stone and fossils are abundant. The Hartwell Clay is in the Lower Portland. Freshwater Purbeck beds lie below the Portland and Lower Greensand beds; they cap the ridge between Oving and Whitchurch. Glass-making sands have been worked from the Lower Greensand at Hartwell, and phosphatic nodules from the same beds at Brickhill as well as from the Gault at Towersey. A broad band of Gault, a bluish clay, extends from Towersey across the county in a north-easterly direction. Resting upon the Gault is the Upper Greensand; at the junction of the two formations numerous springs arise, a circumstance which has no doubt determined the site of several villages.
The Chalk rises abruptly from the low lying argillaceous plain to form the Chiltern Hills. The form of the whole of the hilly district round Chesham, High Wycombe and the Chalfonts is determined by the Chalk. Reading beds, mottled clays and sands, repose upon the Chalk at Woburn, Barnham, Fulmer and Denham, and these are in turn covered by the London Clay, which is exposed on the slopes about Stoke Common and Iver. Between the Tertiary-capped Chalk plateau and the Thames, a gentler slope, covered with alluvial gravel and brick earth, reaches down to the river. Thick deposits of plateau gravel cover most of the high ground in the southern corner of the county, while much of the northern part is obscured by glacial clays and gravels.