The Geographical Journal (Journal of the Royal Geographical Society): Volume XII, No. 2 [‎269v] (41/154)

132 THE ANNUAL RANGE OF TEMPERATURE IN THE SURFACE WATERS OF THE
with massive shells gradually disappear, or are represented by small
dwarfed species. In the cold polar waters the predominant animals
belong to the hydroida, holothurioidea, annelida, amphipoda, isopoda,
and tunicata, in which there is a feeble development of carbonate
of lime.
The secretion by calcareous organisms of the practically insoluble
carbonate of lime from the soluble sulphate of lime in sea-water can
scarcely be regarded as wholly a direct life process, in so far as it is
capable of proof that the reaction results from the decomposition of the
calcium sulphate by ammonium or methylamine carbonate, secreted
by these organisms in place of urea, as in the Mammalia. Of course,
in lime-secreting animals the metabolism gives rise to the formation
of either ammonium or methylamine carbonate, or other nitrogenous
bodies which quickly decompose and yield ammonium carbonate. It is
the waste or effete products of the animal itself which become the sole
factor in the building up of the structures known as coral and shell.
This point has been satisfactorily investigated by the experiments made
by Murray and Irvine at the Granton Marine Station. With regard to
the condition of the carbonate of lime so formed, it is an interesting
and important fact that it is modified in an extraordinary degree by
differences of temperature. For example, if, in imitation of nature, we
add to sea-water neutral ammonium or methylamine carbonate in the
proportion which will decompose the calcium sulphate present, and
expose one portion of the mixture to a temperature of 80° Fahr., so as
to represent the heat of equatorial waters, and expose another portion of
the mixture to a temperature of 45° Fahr., so as to represent the cold
zones of the sea, we find that in the warm water the separation of car
bonate of lime begins almost at once, and takes the aragonitic form,
whereas in the cold water it begins only after the lapse of a few hours,
and is precipitated as well-defined rhombohedral crystals, similar to
crystals of calcspar, so that in eight hours the amount of carbonate of
lime thrown out of solution in the warm water is about twelve times
that in the cold water. When we take into account the increased
metabolism of organisms living in water at a temperature of 80° to 90°
Fahr., as against the decreased metabolism of those living in colder
waters, the abundant secretion of carbonate of lime which takes place
in tropical waters, as compared with that in the cold waters of the
arctic and antarctic regions, is readily explained. Another interesting
circumstance is the greater solubility of lime and some of its salts
in cold than in hot water, which fact assists in explaining the increase'
of calcareous deposition in warm seas over that known to take place in
colder regions.*
* Murray and Irvine, “ On Coral Reefs and other Carbonate of Lime Formations in.
Modern Seas” {Proc. Boy. Soc. Edin., voh xvin pp. 79-109) r 1890.