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in Hertfordshire and elsewhere may, as suggested by Prof. Hughes, be of Pliocene age, but this view depends very much upon the position of the boundary-line taken between Pliocene and Glacial deposits. (See p. 312.)
The deposits of shelly sand called Crag' which occur on the eastern borders of Norfolk, Suffolk, and Essex, have long been known, but for the minute description and identification of their Molluscan remains we are indebted to Mr. Searles Wood, sen., while we owe our knowledge of the detailed structure of the deposits very largely to Mr. Wood, jun.
Forty years ago, however (1835), Mr. Charlesworth gave the first good account of the Crags in Suffolk, and he then proposed the terms · Red Crag' and · Coralline Cray' to distinguish them from one another, and from the Norfolk or Norwich Crag, to which he subsequently applied the term Mammaliferous Crag.
Since this date the labours of Messrs. S. V. Wood, jun., F. W. Harmer, the Rev. 0. Fisher, Prestwich, and some others, have added greatly to our knowledge of the Pliocene strata, and the following stratigraphical divisions are now generally adopted—the upper part of the Red Crag being considered as the representative of the Fluvio-marine Crag :5. Bure Valley Beds.
Norwich Crag or
} (Older Pliocene.)
Classed as Lower Glacial by Wood and Harmer. (See p. 308.)
SUFFOLK CRAG, WHITE CRAG, or BRYOZOAN CRAG.'
The Coralline Crag consists of a series of calcareous shelly sands, sometimes marly, and having a thickness of from 40 to 60 feet.
The following general divisions are abbreviated from those given by Mr. Prestwich : 7. Sand and comminuted shells, with remains of Bryozoa, sometimes
forming a soft building-stone, showing much false-bedding. 6. Sand with small shells and seams of comminuted shell. 5. Sands with numerous Bryozoa, often in the original position of
growth, and containing also small shells and Echini. 4. Comminuted shells, large entire or double shells, and bands of
limestone. 3. Marly beds with well-preserved shells. 2. Comminuted shell-beds with Cetacean remains and Bryozoa. 1. Bed with Phosphatic nodules, called “Coprolites,' and mammalian
remains,-called the Suffolk Bone-bed. The Suffolk bone-bed, or · Coprolite bed,' has been described by Mr. E. Ray Lankester as being a bed from half a foot to three feet in thickness, and lying upon the London Clay in Suffolk wherever the Red Crag or the Coralline Crag is found. It is composed of rounded phosphatic nodules called coprolites,' and water-worn teeth and bones of Mastodon, Rhinoceros, Tapir, Bear, Whale, and Shark. Mr. Lankester considers that the Cetacean remains were derived from the older crag-deposit found in Belgium, and known as the Diestien oz Black-crag.
The beds at the base of the Red Crag may, however, have
1 The term Bryozoan Crag was proposed, because there are few Corals in this Crag, the forms which led to the proposal of the term Coralline being Bryozoa or Polyzoa.
2 Mr. Colchester considers the ‘Coprolite' bed to be the débris of a bed intermediate in age between the London Clay and the Coralline Crag.
been derived from those formed at the time of the Coralline Crag. (See p. 285.)
In the Suffolk Bone-bed are found rounded masses and nodules of sandstone termed Box stones, which sometimes contain fossils. Mr. Lankester has remarked on their resemblance to the Lenham sandstones. (See p. 264.)
The Coralline Crag is well shown in the neighbourhood of Woodbridge, Aldborough, and Orford, at Sutton, Ramsholt, Sudbourne, Broom Hill, Gedgrave, &c.
Amongst the fossils are Cypræa Europcea, Voluta Lamberti, Turritella incrassata, Fusus consocialis, F. gracilis, Scalaria clathratula, Natica, Calyptræa Chinensis, Fissurella Græca, Anomia ephippium, Ostrea edulis, Pecten opercularis, P. maximus, P. Gerardii, Pinna pectinata, Pectunculus glycimeris, Nucula nucleus, Lucina borealis, Diplodonta rotundata, Cardita senilis, C. scala is, Asturte Omalii, A. gracilis, Cyprina Islandica, C. rustica, Venus casina, Panopæa Faujasii, Terebratula grandis, Balanus crenatus, Fascicularia, Cladocora, Turbinolia, Echinus Woodwardi, Heteropora pustulosu, Cellepora ellas, &c.
Mr. Wood considers that the Coralline Crag was deposited in the sea at no depth greater than 300 feet.
This deposit consists generally of dark red shelly sand, often exhibiting false-bedding or oblique lamination, and having a thickness of about 25 feet. Sometimes the colour is yellow, brown or grey. Seams of laminated clay are occasionally met with. Mr. S. V. Wood, jun., has, however, shown that the deposit is structurally divisible into five stages, of which the 1st, 2nd, 3rd, and 4th (counting upwards) were not deposited under water ; but from their being regularly laminated, at angles varying between 25° and 35°,
possessing (with the exception of the 2nd) an unvarying direction in every stage, he regards them as the result of a process of • beaching up,' by which was formed a reef extending from the river Alde on the north, to the southern extremity of the deposit in Essex. Of these four stages, the 4th is the most constant and important, the 1st, 2nd, and 3rd being frequently either concealed by, or destroyed during the formation of, the succeeding stages. At Walton-on. Naze alone do any of the four lower stages contain evidence of being a subaqueous deposit; there the 1st stage is so, but it is covered by two reef stages, and these again by the 5th stage.
The 5th stage is invariably horizontal, and contains evidence of having been formed under water. This stage is developed in such a way as to show that it was formed in channels eroded in the older reef, and it is at its base that the coprolite workings occur.
Owing, however, to the probable reconstruction or reaccumulation of different stages, Mr. Wood considers it impossible to separate the Red Crag in general, into all those chronological divisions of it that may exist, but there are three divisions that are very clearly indicated :3. Scrobicularia Crag Largely made up of Tellina pretenuis, and T.
obliqua, with also Scrobicularia pluna. 2. Deben, Orwell, and Butley Red Crag, with northern forms of mollusca
predominating 1. Walton (irey and Red Crag, containing many species characteristic of
the Coralline Crag.
The Scrobicularia Crag comprises beds which gradually lose both the red colour and the oblique bedding as we ascend the section, and become horizontal in the upper layers.
The Red Crag is well shown at Walton-on-the-Naze, Sutton, Ramsholt, Trimley, Bawdsey, Butley, Hollesley, &c.
Near Aldborough and at Park Farm, Tattingstone near Ipswich, the Red Crag may be seen in section superimposed upon the Coralline Cray,
A bed of phosphatic nodules called coprolites' often occurs at the base of the Red Crag, and with it are found fragments of septaria from the London Clay, Chalk flints, Greensand chert, rolled or water-worn bones and teeth of Cetacea, Sharks (Carcharodon megalodon), &c. According to Mr. Prestwich seams of phosphatic nodules, or dispersed nodules, may be found through the whole of the Red Crag; and all of them were probably derived from the Coralline Crag. Ainong the Cetacean bones are the earbones of Whales, while other derived fossils are Crustacea from the Loudon Clay.
The coprolites' yield from 45 to 60 per cent. of Phosphate of Lime: they have been worked near Sutton, Boyton, Butley, Trimley, Bawdsey, Shottisham, &c. The beds are however becoming exhausted. (See p. 244.)
The question whether some of the forms characteristic of the Coralline Crag may not be derived from older deposits, is important, but, according to Mr. Wood, it is a still more complicated problem whether or not the fossils of the Red Crag in its various stages have a derived origin.
The fossils of the Red Crag include the Prophon (Fusus) antiquum, of which the sinistral or left-sided form (var. contrarium), according to Mr. Wood, is found in the Walton Crag, while the dextral form abounds in the rest of the Red Crag. Other fossils are Pecten opercularis, Pectunculus glycimeris, Mactra arcuata, M. ovalis, Tellina obliqua, Cardium edule, C. angustatum, Mytilus edulis, Nassa reticosa, Buccinum tenerum, B. undatum, Natica catena, N. multipunctata, Purpura tetragona, P. lapillus, Turritella incrassata, &c.
In the famous sections at Chillesford the Scrobicularia Crag rests upon the Red Crag (of Butley), and is directly
Many fossil bones and teeth washed out of the Red Crag may be picked up on the beach at Harwich and Walton.