790 REPORT—1896. 
Tt follows from this that the calcareous parts of the inhabitants of the ‘denthos” 
would be liable to solution during life, unless (a) they were protected by the flesh 
of the animal or by epidermis, or (4) they consisted of Calcite. 
The deep-sea mollusca are mainly composed of Aragonite, but they generally 
have an extremely thick epidermis. The deep-sea calcareous corals are almost 
exclusively simple forms, and the lower portion of stony structure is gradually left 
bare as the creature grows. All the forms examined by the author, eg., Caryo- 
phyllia, Parasmilia, Cyclocyathus, Stephanophyllia,! are of Calcite, whereas nearly 
all reef-building Actinozoa produce Aragonite structures. 
The effects of solution upon the nature and distribution of deep-sea deposits.— 
Deep-sea deposits are mainly derived from two sources: (a) land detritus and vol- 
canic ejecta carried seaward by currents; (4) remains of free-swimming pelagic 
organisms. Inshore the deposits usually contain a large percentage of detrital 
materials, while towards the deep the organic remains tend to preponderate. As 
the water deepens another factor, solution, comes into play, and the calcareous 
elements of the deposits are progressively removed by solution. The solution is, 
according to Murray, Agassiz, and others, effected in part during the slow sinking 
of surface organisms, and in part while lying upon the floor of the ocean. Agassiz 
assigns the greater importance to solution during descent, but the fact recorded by 
him, that ‘the more numerous the shells are in the surface waters, the greater 
is the depth at which they will accumulate at the bottom,’ seems to show that 
solution at the bottom is very considerable. In the profoundest depths the deposits 
consist almost wholly of non-caleareous materials. Two principal calcareous 
deposits occur below 500 fathoms, viz., Globigerina ooze, which covers 49} million 
square miles of the ocean floor and has a bathymetric range from 400 to 2,925 
fathoms, and Pteropod ooze, which is a Globigerina ooze characterised by the 
presence of a large number of shells of Pteropods and Heteropods. It occurs only 
where the surface waters are warm, and hence is limited to tropical and sub- 
tropical regions. It covers an area of 400,000 square miles, and ranges in depth 
from 395 fathoms to 1,525 fathoms, below which the Pteropod shells disappear, 
leaving a normal Globigerina ooze. It is generally agreed that the limitation in 
depth of the Pteropod remains is due to solution, for the living Pteropods swarm 
over the surface in prodigious numbers, whatever be the depths below. 
Agassiz succinctly states the facts as follows: ‘The Pteropod and Heteropod 
shells are the first to disappear from deposits, then the more delicate surface 
Foraminifera, and finally the larger and heavier ones.’ The fact that these rela- 
tively large shells wholly disappear by solution under conditions that the minute 
Foraminifera survive is beyond doubt, and demands explanation. Several explana~ 
tions have been proposed. Fuchs in 1877 suggested that Globigerina might be 
composed of Calcite and the Pteropods of Aragonite, and the author independ- 
ently made the same suggestion. Dr. Murray and the Abbé Renard, however, 
rejected that hypothesis, and considered that the Globigerina survived by reason 
of their greater thickness. 
The author, with the assistance of Mr. Albert Jowett, a student in the 
Geological Laboratory of the Yorkshire College, has made a number of determina- 
tions of the relative thickness of Globigerina and Orbulina, the most characteristic 
Foraminifera of the deep-sea oozes and of Styliola and Cavolinia as representing 
the Pteropods. He failed to find any such difference of thickness as would account 
for the much greater durability of the Foraminifera, the range of thickness of the 
two classes being practically identical. It may be represented by the numbers 
2-6°5 in each case. 
The mineral constitution was also successfully determined. Prof. W. J. 
Sollas determined the sp. gr. of Globigerina by an extremely ingenious adaptation 
of heavy solutions to be approximately that of Calcite. This has been confirmed 
by the author, who has also obtained a uniaxial optical figure from specimens of 
Orbulina, showing that the low sp. gr. is due to Calcite constitution, and not to 
the presence of animal matter. 
1 These are corals of deep-sea types from the Cretaceous rocks, 
