WHITE OR CORALLINE CRAG. 
197 
brown nodules, first noticed by Professor Henslow as con¬ 
taining a large percentage of earthy phosphates. This bed 
of coprolites (as it is called, because they w^ere originally 
supposed to be the feces of animals) does not always occur 
at one level, but is generally in largest quantity at the junc¬ 
tion of the Crag and the underlying formation. In thick¬ 
ness it usually varies from six to eighteen inches, and in some 
rare cases amounts to many feet. It has been much used in 
agriculture for manure, as not only the nodules, but many of 
the separate bones associated with them, are largely impreg¬ 
nated with phosphate of lime, of which there is sometimes 
as much as sixty per cent. They are not unfrequently cov¬ 
ered with barnacles, showing that they were not formed as 
concretions in the stratum where they now lie buried, but 
had been previously consolidated. The phosphatic nodules 
often include fossil crabs and fishes from the London clay, 
together with the teeth of gigantic sharks. In the same bed 
have been found many ear-bones of whales, and the teeth of 
Mastodon arvernensis^ Rhinoceros Schleiermacheri^ Tapirus 
prisciis^ and Hipparion (a quadruped of the horse family), 
and antlers of a stag, Cervus anoceros. Organic remains also 
of the older chalk and lias are met with, showing how great 
was the denudation of previous formations during the Plio¬ 
cene period. As the older White Crag, presently to be men¬ 
tioned, contains similar phosphatic nodules near its base, those 
of the Red Crag may be partly derived from this source. 
White or Coralline Crag. —The lower or Coralline Crag is 
of very limited extent, ranging over an area about twenty 
miles in length, and three or four in breadth, between the 
rivers Stour and Aide, in Suffolk. It is generally calcareous 
and marly—often a mass of comminuted shells, and the re¬ 
mains of bryozoa* (or polyzoa), passing occasionally into a 
soft building-stone. At Sudbourn and Gedgrave, near Or- 
ford, this building-stone has been largely quarried. At some 
places in the neighborhood the softer mass is divided by thin 
flags of hard limestone, and bryozoa placed in the upright 
position in which they grew. From the abundance of these 
coralloid mollusca the lowest or White Crag obtained its 
popular name, but true corals, as now defined, or zoantharia, 
are very rare in this formation. 
* Ehrenberg proposed in 1831 the term Bryozoum, or ‘‘ Moss-animal,” for 
the molluscous or ascidian form of polyp, characterized by having two open¬ 
ings to the digestive sack, as in Eschara, Flustra^ Retepora^ and other zo¬ 
ophytes popularly included in the corals, but now classed by naturalists as 
mollusca. The term Polyzoum^ synonymous with Bryozoum^ was, it seems, 
proposed in 1830, or the year before, by Mr. J. O. Thompson. 
