CORALLINE CRAG. 
25 
sands, in some places more or less marly, which are rich in 
Molluscan remains. The second consists of a solid bed formed of 
Molluscan remains, agglutinated with the fronds and fragments 
of various species of Polyzoa into a rock^ so hard as to have been 
formerly quarried for building. The third and uppermost is a 
thin subsidiary bed, consisting of a few feet of the abraded material 
of the rock, reconstructed evidently in very shoal water, probably, 
indeed, between tide marks, as it is very obliquely bedded. 
From the outliers at Tattingstone and Ramsholt this rock-bed 
is absent, but over the Sutton outlier a small cap of it remains 
Over the main mass, however, it spreads continuously, and either 
from a slight northerly dip of the whole formation, or else from a 
displacement of the underlying shelly sands, this rock-bed descends 
to the sea-level at the northern extremity of the mass.’^ The 
authors then criticise the method by which an estimated thickness 
of between 80 and 90 feet had been obtained for this formation, 
and consider that the place to test the true thickness of the 
formation is clearly that where it is in the greatest state of pre¬ 
servation. ..... Estimated in this way, it will be ditlicult 
to make out the thickness of the Coralline Crag as exceeding 
sixty feet.^" 
Messrs. Wood and Harmer object to Professor Prestwich’s 
division of the lowest portion, the shelly sands, into constant and 
determinable horizons, characterized by special groups of fossils, 
and remark that the author of the ‘ Crag Mollusca ’ in his long 
researches has mainly conhned himself to one pit at Sutton, afford¬ 
ing a vertical range of but a very few feet, and yet from this spot 
he has obtained specimens of nearly the whole known species of 
the Coralline Crag, many of these being known to collectoi’s 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/’ 
Prof. Prestwich had estimated the depth of water under which 
this Crag was accumulated at “ possibly from 500 to 1,000 feet;” 
but S. V. Wood, sen., 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 35 or 40 fathoms, 
so that, coupling the physical difficulties with the exigencies of 
the molluscan evidence, we may, we think, regard the depth of 
the Coralline Crag sea of Suffolk as under 300 or even 250 feet, 
rather than as approaching 1,000.” 
In the same year (1872) Messrs. A. and P. Bell gave some 
additional details of certain of the Coralline Crag sections, and a 
long catalogue of the fossils from the Lower Crag,” as the 
Coralline Crag is named in their papers.* 
On the English Crags and the Stratigraphical Divisions indicated by their 
Invertebrate Fauna. Proc. Geol. Assoc., vol. ii. No. 5, p. 185. Supplement by 
A. Bell, No. 6, p. 270, and The Succession of the Crags. Geol, Mag., vol. ix.p. 209. 
