ON THE BRITISH FOSSIL CORALS. viv A 
REPORT. 
The researches of Darwin, Dana, and others have been so long before the 
scientific world, that the external physical conditions accompanying Coral- 
life are universally well understood. The physico-chemical changes which 
take place in dead corals and influence their future fossil condition have been 
described ; and it is most reasonable to assert that the representatives of the 
existing Coral-faune flourished under the same kind of conditions, and were 
subjected to the same prefossil incidents and changes. 
Corals are either aggregated in reefs or distributed sparely over the sea- 
bottom. In the strata of nearly every formation, somewhere or other, 
aggregations of corals are found, either in great banks, or as distinct reefs 
hanging on to the older rocks; moreover sparely distributed solitary or 
simple forms are universal. 
In the Caribbean Sea, the Indo-Pacific, the Great Ocean, the China seas, 
aggregations occur and the species flourish in comparatively shallow water. 
In the deep water from 50 to 200 fathoms, between reefs, simple and sparely 
distributed species occur ; and in other seas, where there are no reefs, the sea- 
bottom from about 50 to 200 fathoms supports larger or smaller simple and a 
few compound forms. 
The Mediterranean, the Atlantic off the Spanish coast, the Bay of Biscay, 
the South-west British sea, and especially the seas between Unst and 
Norway are characterized by numerous simple Madreporaria and a few com- 
pound forms. 
This geographical and bathymetrical distribution must influence us in 
reasoning geologically upon the presence of corals in strata; and a tropical 
climate must not be of necessity inferred from the discovery even of fine 
specimens. 
Corals cannot migrate except by the floating away of their ova; and very 
slight alterations in the very definite physical conditions destroy the parent 
stock as well as the ova. It is not surprising therefore to find the species very 
much restricted in their vertical range in strata. Recent species vary greatly 
under slight modifications of the sea-depth, force of wave, and purity of sea- 
water ; and it is found that corresponding variations occurred in every age, 
the minute structural differences repeated over and over again in specimens 
from the same deposits having clearly a genetic relation to a definite type. 
As there are now geographical provinces of corals differing in genera, species, 
and in physical peculiarity, so in every formation down to the Lower Silu- 
rian there are evidences of areas characterized by reefs or by simple and 
solitary species, and the species of distant localities were, as now, different, 
peculiar, and occasionally identical. From those early days there have been 
opportunities for the migration of distant species by their ova; and it is 
found that the fossil species peculiar to a certain geological horizon in one 
part of the world are often represented by closely allied species, varieties, or 
identical forms in higher or lower horizons in other parts. Some few 
forms are very persistent ; and those which have lasted through the Tertiary 
ages into the present have a great geographical range, just as those which 
had a great vertical range in older deposits had also a great horizontal area. 
It is necessary, in considering the relative ages and contemporaneity of 
coral species, to remember that a coral reef on the side of a precipitous sub- 
merged mountain-top had its débris carried down the abyss for ages, and 
that this is enormous in amount. 
It must be remembered that in the course of time the distance between 
