iv SUPPLEMENT TO THE CRAG MOLLUSCA. 



in his long researches has mainly confined himself to one pit at Sutton, affording a vertical 

 range of bat a very few feet, and yet from this spot he has obtained specimens of nearly the 

 whole known species of the Cor. Crag, many of these being known to collectors as 

 occurring only at the pits near Orford. Not only this, but so inconstant is the Molluscan 

 facies at any one place, that many species which once occurred at this spot (and some of 

 them abundantly) have not been noticed there for many years. An attempt under such 

 circumstances to group these shelly beds in any order of Molluscan succession would 

 thus evidently be illusory. At this spot, moreover, Foraminifera were once abundant, and 

 from it Mr. Wood collected all the species obtained by him from the Cor. Crag which are 

 described in the Monograph of Messrs. Jones and Parker. No Eoraminifera, however, 

 have been found by him there for many years, although very many tons of the Crag 

 from the same spot have been sifted by him for Mollusca during that period. 



The depth of water under which this Crag was accumulated has been estimated by 

 Mr. Prestwich at " possibly from 500 to 1000 feet." Against this view there are, it 

 seems to us, objections. A depth of 1000 feet would have carried the Crag sea over the 

 whole of East Anglia, and, indeed, across England, 1 and it is unlikely that all traces of 

 such a sea should have been so completely removed as to present the blank which now exists. 

 At elevations of about 350 feet (*. e. fifty-eight fathoms), some pebble beds occur through 

 Southern Essex, which might represent the shingle of the southern shore of a sea having 

 a depth of about sixty fathoms over Suffolk, and these might belong to the age of the 

 Coralline Crag, but these seem better to associate themselves with the Bagshot beds on which 

 they rest than to any later formation. 2 The author of the ' Crag Mollusca ' considers that 

 nothing among the forms of Mollusca yet obtained from the Crag, points to the existence 

 of any greater depth of water for their habitat than thirty-five or forty fathoms ; so that, 

 coupling the physical difficulties with the exigences of the Molluscan evidence, we may, 

 we think, regard the depth of the Cor. Crag sea of Suffolk as under 300 or even 250 

 feet, rather than as approaching 1000. 3 



1 Some traces occur on the North Downs of Kent of beds supposed by some to belong to the oldest 

 Crag, or Diestien formation. These are by the Geological Survey assigned to sands beneath the London 

 Clay ; but if they be of Crag age, there has, we contend, been a great upheaval in this part of England in 

 Post-glacial times, which has quite changed the relative levels of the Crag period. 



2 See ' Quart. Journ. Geo. Soc.,' vol. xxiv, p. 461, and also the forthcoming new edition of the 

 Memoir of the Geological Survey on sheets 1 and 7, in which the view^of their Bagshot age is adopted. 



3 The line of GOO feet is now distant between 350 and 600 miles from the Suffolk coast. The deepest 

 parts of the North Sea between Suffolk and the Dutch coast are but 180 feet, while the depth of the chief 

 part of that sea ranges between tide marks and 150 feet. Messrs. Jones and Parker, in the introduction 

 to their Monograph (p. 3), say, in reference to the Coralline Crag Foraminifera, that they are best repre- 

 sented by dredgings between 300 and 420 feet south of the Scilly Isles, and from the Mediterranean at 

 126 feet. This small depth in the Mediterranean is significant, as it is with the Mediterranean that the 

 Molluscan Fauna of the Coralline Crag has its chief affinity. 



The Entomostraca throw no light on the subject, as Mr. Rupert Jones, according to the revision of the 

 Monograph of himself, Mr. Parker, and Mr. Brady, made by him in the ' Geol. Magazine' (vol. vii, p. 155), 



