MIDFORD SANDS.

The term Midford Sands was given in 1871 by Prof. Phillips to the Sands which occur between the Upper Lias Clay and the Inferior Oolite. The fauna of the Sands connects them as closely with the Lias as with the Oolites, and in their lithological characters they exhibit no very marked break; they are transitional, but perhaps more nearly allied to the sandy Oolite above, and therefore it is well to place them with the Oolitic series. In some localities the passage into the Lias appears to be very gradual, and in others the passage into the Oolites; but as a rule the base of the sandy beds is indicated by a line of springs thrown out by the Lias clays, and by a marked feature in the conformation of the ground.

Considerable palæontological changes, and some mineralogical changes, take place when the beds are traced across the country; and although the sandy condition prevails generally in the same position above the Upper Lias clay from Yorkshire into Dorsetshire, and the beds may strictly be termed homotaxeous, yet in places they partly represent other formations, and different names have been given to the series.

Thus Prof. Phillips remarks that in the long range from the coast of Dorsetshire to the coast of Whitby the character of the lower sand varies, and especially in colour. Through Oxfordshire, Rutland, Lincoln, and the southern part of Yorkshire, it is a very dark brown ferruginous rock, whence it is often called 'gingerbread stone,' frequently enclosing shelly concretions (Banbury), occasionally enveloping beds of limestone, and sometimes (Northampton, Rockingham) interlaminated by white beds of oolite. In some places, especially in Lincolnshire, it consists of an alternating series of white

and brown sand. Ironstone occurs in Northamptonshire and Oxfordshire.

We therefore have the Midford Sands of Dorsetshire, Somersetshire, and Gloucestershire; the Northampton Sands in the Midland Counties (which partly represent the Inferior Oolite and partly the Great Oolite); and in Yorkshire the sands beneath the Dogger (Blue Wick Sands), seen at Peak, Blue Wick (or Wyke) Bay, having a thickness of upwards of 50 feet. (See p. 177.)

It is only right to mention that Prof. Buckman considers the Dorsetshire sands to represent (palæontologically) portions of the Inferior Oolite of Gloucestershire; and that Mr. Judd has observed that the Northampton Sands sometimes rest on an eroded surface of the Upper Lias Clay,' a feature which Mr. Moore has noticed locally between the Midford Sands and Upper Lias, near Yeovil.

Midford is a little hamlet about three miles south of Bath, and it was there that William Smith first studied the Sands, and called them the Sand of the Inferior Oolite.'

They are very well developed at Nailsworth and Frocester, and the names of these places have been locally used to designate the Sands.

They consist of micaceous yellow sands, with occasional beds of concretionary sandstone or sandy limestone called 'sand bats' or sand burrs,' which sometimes contain organic remains and they are capped by a brown marly iron-shot limestone, one to three feet in thickness, which yields numerous species of Ammonites, Belemnites, and Nautili, whence the bed has been termed by Dr. Wright the Cephalopodabed;'2 while the series has been termed the Ammonite sands' by Mr. Hull.

6

1 He states that as yet we have no conclusive evidence that any part

of the Northampton Sand represents the Midford Sand.

2

* Dr. Wright termed the series Upper Lias Sands.'

Amongst the fossils Ammonites Jurensis is conspicuous: hence the formation has been termed the zone of A. Jurensis by Dr. Wright.

Rhynchonella cynocephala is another characteristic fossil: hence the term 'Cynocephala stage' used by Mr. Lycett.

The sands contain also Ammonites radians, A. hircinus, A. variabilis, A. Aalensis, Cucullaa, Gervillia Hartmanni, &c.

The fossils belong partly to the Lias and partly to the Inferior Oolite, and Prof. Phillips has well observed that 'before the Liassic life has come to an end, the Oolitic life has begun.'

That this change was not contemporaneous over the area. embraced by Gloucestershire, Somersetshire, and Dorsetshire, seems to be borne out not only by palæontological differences, but by the varying thickness and occasional entire disappearance of the Midford Sands themselves.

To the east of Bridport Harbour there is a magnificent coast-section of the Sands, which there attain a thickness of probably 200 feet. On the other side of the Harbour the Sands likewise occur, overlaid almost directly by the Fuller's Earth, as the Inferior Oolite is extremely thin.

The beds are well exposed in the neighbourhood of Sherborne (140 feet) and Yeovil. They cap the summit of Glastonbury Tor and Brent Knoll (Cephalopoda-bed).

In Somersetshire, south of the Mendips, the thickness of the sands is about 160 feet.1 North of the Mendips the thickness is very variable, and the sands disappear entirely in places. At Bath their thickness is about 40 feet; they have been well exposed in the tunnel under Combe Down.

In Gloucestershire the Sands and Cephalopoda-bed are persistent, and have a thickness of from 30 to 40 feet. The Cephalopoda-bed is sometimes bored by Lithodomus.

1 Called 'Brim Sand' at Ham Hill, near Yeovil.

NORTHAMPTON SANDS AND LOWER ESTUARINE SERIES.

These beds consist of sand and sand-rock, containing much iron-ore, and having a thickness of from 20 to 80 feet. Mr. S. Sharp has noted the following divisions of the beds in the Northampton district :

4. White or grey sand,' and sandstone sometimes quarried for building-stone, containing a plant-bed (Lower Estuarine Series)

3. Thin beds of ferruginous sandstone and shelly calcareous beds— very variable, being sometimes entirely calcareous, at others consisting of white sand and sandstone

2. Coarse oolitic limestone

1. Ironstone-beds containing Rhynchonella variabilis, R. cynocephala,

At Banbury the beds are only 12 feet in thickness.

Feet

12

30

4

35

Amongst other fossils from the Northampton Sands are:Avicula Braamburiensis, Gervillia acuta, G. Hartmanni, Hinnites abjectus, Lima duplicata, Ostrea gregaria, Pecten personatus, P. demissus, Astarte elegans, Cardium Buckmani, Ceromya Bajociana, Cucullaa cancellata, Trigonia costata, Terebratula perovalis, Nerinaa cingenda, Belemnites giganteus, and Ammonites Murchisona.

Amongst the localities where the beds may be observed are Kingthorpe, Northampton, Duston (slaty beds), Blisworth, and Gayton.

The Ironstone-beds yield a number of fossils, many of them, as Mr. Sharp points out, cast, as it were, in iron, so that the introduction of the ore must have taken place subsequently by infiltration and replacement.

The ore yields 40, and sometimes 55, per cent. of pig

1 Clay-beds in this series have been worked for Terra-cotta in the neighbourhood of Stamford. Concretionary masses of sandstone called Pot-lids' are met with in the sands.

iron. It is worked at Duston, Blisworth, Gayton, Wellingborough, Cranford, Stamford, &c.

The Northampton sands include the Lower Estuarine series of Mr. Judd, which embraces the brown and white sands with argillaceous beds and plant-remains that occur above the fossiliferous Ironstone-beds.

In the northern part of Oxfordshire and south Northamptonshire, the Northampton Sands are considered by the Geological Survey (chiefly through Mr. Judd's investigations) to be the equivalent of the lower zone of the Great Oolite and part of the Inferior Oolite; while in the northern part of Northamptonshire and in Lincolnshire they include the Lower Estuarine series, and occur beneath the Collyweston Slates and Lincolnshire Limestone (Inferior Oolite). The Northampton Sand forms a rich soil.

Origin of the Northampton Sand.-The following conclusions as to the origin of the Northampton Sand and Ironore, which have been so carefully worked out by Mr. Judd, may be introduced here, as they may serve to throw light on the origin of similar deposits of other periods :-1

We find, in what is now the Midland district of England, and at a period separated by a long interval of time from that of the last deposit in the area, the Upper Lias Clay, that a number of considerable rivers, flowing through the Paleozoic district lying to the north-west, formed a great delta. Within the area of this delta the usual alternations of marine, brackish-water, and terrestrial conditions occurred, and more or less irregular accumulations of sand or mud, in strata of small horizontal extent, took place. Subsequently, and probably in consequence of the gradual depression of the area, the conditions were changed, and in an open sea of no great depth, by the abundant growth of coral reefs and the accumulation of dead-shell banks during enormous periods of time, the materials of the great deposits of the Lincolnshire Oolite limestone were formed. On a re-elevation of the area the former estuarine conditions were also reproduced, and similar deposits, but of an argillaceous rather than an arenaceous character, were formed. Confining our attention to the earlier

Geology of Rutland, &c. (Mem. Geol. Surv.)