In 1891 Mr. A. Strahan drew attention to the occurrence of two bands of phosphatic chalk in the neighbourhood of Taplow Court.[1]
These bands consist of brown friable chalk, the colour being due to a multitude of brown grains in a white chalky paste. The grains are almost entirely of organic origin, foraminifera, fragments of Inoceramus and of teeth and bones of fishes, together with small oval pellets which are evidently coprolites of small fishes forming the bulk, all being more or less phosphatic. Two bands occur, the higher is from 8 to 1 1 feet thick, and occurs at about 20 feet from the base of the Eocene strata as proved in a shaft. The lower band is 4 feet thick and occurs from 1 2 to 19 feet lower, according to measurements made in the shaft section and in a pit near the lodge of Taplow Court. Mr. Strahan observes that there can be little doubt that this phosphatic chalk underlies a con- siderable part, if not the whole, of the outlier of Tertiary strata on which Taplow stands, but there are no other sections to prove its exten- sion. Hence it appears to be strictly local. Analysis showed from 18 to 35 per cent of phosphate of lime.
The Taplow phosphatic chalk bears a strong resemblance to a bed, approximately on the same horizon, which has been worked in the north of France.
At Taplow the Chalk has yielded Actinocamax (Belemnitella) quadratus, Ostrea acutirostris and other fossils, rather above the zone of Marsupites.
The sloping chalk plateaus, formed mainly of Upper Chalk, are mostly under arable cultivation, but owing to their coverings of loam and gravel the soils are often deficient in lime. Hence it has been the custom to sink wells or pits in the fields to a depth of 15 or 20 feet to obtain chalk for the land. The steeper slopes of Upper and Middle Chalk form down land with a herbage adapted for sheep walks. Here the soil is thin, and although the ploughed fields may show a brown clayey or loamy soil, adjacent pits often exhibit but a trace of soil.
Plantations of beech trees occupy many tracts in this area on the borders of the plateaus and along the deep and ramifying valleys. These beech woods furnish material for the important chair manufactory at High Wycombe, and for sundry wooden articles made at Chesham and elsewhere. The celebrated Burnham Beeches are situated partly on gravel and partly on Reading Beds, but no doubt in places they are rooted into the underlying Chalk which appears at the surface to the north-west of Burnham Common.
Old terraces of cultivation or lynchets occur in places, as on the hillsides near Chesham, and notably on the Chalk outlier of Southend and of Westend Hill, near Cheddington, where, as I am informed by the Rev. F. W. Ragg, some of the best examples (locally called ' lynces ') may be seen.
The Chalk is a famous water-bearing formation, and the upper
- ↑ Quart. Journ. Geol. Soc. xlvii. 356. For account of the Microzoa see F. Chapman, ibid. xlviii. 514.
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