26 
CORALLINE CRAG. 
S. V. Wood, sen., in his concludinif? remarks at the end of the 
Supplement to the Crag Mollusca'^ (1874), criticises Jeffreys’ 
identifications of many of the Coralline Crag species with recent, 
especially with arctic, forms, and maintains the accuracy of 
most of his own determinations. He observes that “ it is obvious 
that this author’s leanings are very marked, so as to group 
together allied Crag forms as varieties only of one species, and 
especially to make out a Crag shell to be either identical with a 
living species, or, at most, only a variety of it whenever the 
slightest presumption can be found for that course.” Wood also 
points out that “ another reason for not undervaluing even slight 
differences by which many of the Crag Mollusca are separable 
from their living analogues, and so reducing them to the inferior 
importance supposed to be possessed by the term ‘ variety,’ exists 
in the discordance between the evidence presented by the Mol- 
luscan fauna when thus reduced, and that presented by the pther 
organisms of the Crag period.” He, therefore, is still of the 
opinion, held also by Forbes and Hanley, that the Molluscaa 
fauna of the Coralline Crag has its affinities chiefly with that of 
the Mediterranean. To this Monograph is added a Synoptical 
List of the Crag mollusca, in which is also given tlie geographical 
range of all the species which Wood recognizes as still living. 
Jn 1879 Wood published a second supplement to his Mono¬ 
graph, and in 1882, after his death, appeared the third supplement, 
edited by his son. To the third supplement S. V. Wood, jun., 
added some further notes on the physical conditions under which 
the Crag was deposited, and on the correlation with other deposits 
on the continent. 
During the years 1882-3 the maps of the Geological Surveyf 
appeared. These showed the boundaries of the formation more 
accurately than before; but no fresh outliers had been discovered, 
though sunk rocks of Coralline Crag are noted as occurring off 
Thorpe and Sizewell, on the authority of Mr. C. P. Ogilvie. 
Mr. P. F. Kendall,J in 1883, drew attention to the fact that 
whilst the shells in a pit near Aldborough were, with one exception, 
of the kinds determined by Dr. Sorby to have their carbonate of 
lime in the calcite form, the many casts are, without exception, of 
the kinds in which the carbonate of lime is in the form of ara¬ 
gonite. Aragonite, though harder and of higher specific gravity 
than calcite, is a less stable substance, and is much more easily 
acted upon by carbonated water. He adds that “ the consoli¬ 
dation of the Coralline Crag, and the dissolution of the aragonite 
shells, appears to have taken place previously to the deposition of 
the Ked Crag, or at any rate of the middle part of it, as I have 
found a fragment of Coralline Crag with shells and casts in the 
coprolite diggings at Boy ton.” 
During 1885 and 1886 were published the two Memoirs of 
the Geological Survey, in which Messrs. Whitaker and Dalton 
* PalcBontographical Society. 
t Sheets 48 N.E. and N.W., 49 S.W., 50 S.E. 
I Geol. Mag., dec. ii., vol. x. p. 497. 
