
ROCKS 73 
This substance is known in commerce as “rock-guano,” “ rock- 
phosphate,” etc. 
Coprolites are the droppings of fishes, reptiles, or 
mammals, in a more or less fossilised condition. They are 
met with in strata of widely different age, but the coprolites 
of commerce are usually phosphatic nodules, often of a con- 
cretionary nature, and not fossil excrements. Phosphatic 
nodules of this kind sometimes occur in regular beds, as in 
the Upper Greensand and at the base both of the Red and 
the Coralline Crags of England. They are similarly very 
abundantly developed in the neighbourhood of Charlestown, 
South Carolina. 
The origin of these nodules is quite uncertain. They often contain 
fossils, and in some cases are obviously portions of the rock underlying 
the bed in which they occur. In short, they are fragments of some 
calcareous rock, such as Chalk, which have been rolled and rounded, and 
in some way or other have become impregnated with phosphoric acid. 
As this acid may have been derived from marine plants, it has been sug- 
gested that the nodules may have become phosphatised during the long- 
continued growth and decay of sea-weeds. In many cases, however, the 
nodules are certainly of a concretionary nature, and often contain no 
fossils. They are frequently very hard, and may possibly represent the 
residuum of ancient guano-beds—that is, the relatively insoluble constitu- 
ents of such organic accumulations, which have been washed down from 
some neighbouring land. Yet another source of such concretions has been 
suggested. It is known that a small percentage of phosphate of lime of 
organic origin is invariably present in the marine organic oozes which 
have been dredged from great depths, and it has been detected also 
amongst the fine-grained sands and muds which are being accumulated 
around continental shores. It is supposed, therefore, that calcareous 
deposits, such as the phosphatic chalk of this and other countries, may 
have derived their phosphoric acid from a similar source, and that the 
so-called coprolites are simply concretions formed in the usual way by 
aggregation of diffused mineral matter. 
