Chalk and Oolites. Sect. V. Iron Sand.

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throughout tliis stratum in Oxfordshire , and a telliniform shelloccurs in the ironstone of Shotover in Oxfordshire .

The fossils given by Smith in his stratigraphical arrangement,under the head Brick Karth, are partly from this formation,partly from the Folkslone marie; those which have thelocality, Steppingley park, Bedfordshire , are from the iron-sand.

At Shanklin Chine in the Isle of Wight, are nodules of fer-ruginous marie in this formation, containing obscure casts ofturbinated univalve and bivalve shells. The lowest beds alsonear Sandown fort in that island, contain various shells.

The occurrence of vegetable remains in this formation hasbeen already noticed in connexion with the coal beds occa-sionally traversing it: fragments of silicified wood are some-times found.

(d) Range and extent. The tract extending along the footof the chalk hills in Yorkshire , has not as yet received suf-ficient examination to enable us at present to offer any par-ticulars concerning the course of this formation in that quarter,and the marshes and alluvium on the west of that escarpment,in Lincolnshire and Norfolk , generally conceal it. In tin-west of Cambridgeshire , however, we find it well exhibited,and having here once gained a full view of it, we may trace ithence continuously through the remainder of the island. Hereit forms a band nearly four miles broad, between Fenny Stan-ton near St. Ives and Huntingdon, rising into low hills : thisband, still holding the same breadth', preserves a directionnearly south-west through Bedfordshire , crossing that countyfrom Potton to Woburn, and entering Buckinghamshire atBowbrick hills, near Fenny Stratford. Throughout this partof its course, it constitutes the principal mass of a well definedrange of hills, based on the Oxford clay. This chain of hillsis continued through Buckinghamshire in the same direction,from Brick hill on the east to Brill hill on the western border;but the range is here traversed and broken through by nu-merous broad rallies, and thus separated into insulated groups.Throughout all that part of Buckinghamshire which lies westof the Grand Junction Canal, the Aylesbury or Portland lime-stone, which here makes its first appearance underlying theiron sand, forms the lower and central regions of those hills,and the iron sand is confined to their summits. In the valleyjo the south, separating these hills from the chalk range, theprincipal mass of this formation must hold its course ; but thewhole of this tract is so much concealed by debris of flintgravel, derived from the latter, that little can be seen.

In the adjoining county of Oxford, the iron sand and its