MUSEUM OF COMPARATIVE ZOOLOGY. 45 
mineral particles seldom exceeded 0.1 mm. in diameter, but near shore 
they were very much larger, and fragments of rocks and pebbles were 
frequently dredged. Altered fragments of plagioclase, basalts, and dia- 
base were rather frequent. 
The percentage of carbonate of lime in these deposits was usually 
very high, being frequently 70 or 80 per cent, and in the case of a chalk 
rock 90.24 per cent. Where the shores were composed of volcanic or 
other rocks not calcareous, the débris of these made up the larger part 
of the deposits, which might be called voleanic muds. But the majority 
of the deposits should be termed Pteropod or Globigerina oozes, owing 
to the large number of these organisms present in them. It should be 
remembered, however, that both in the size of the mineral particles and 
in the nature of a large number of the calcareous particles, these de- 
posits differ considerably from similar deposits found far away from land 
in the open ocean and called also Pteropod and Globigerina oozes. 
The siliceous organisms never make up more than four or five per 
cent of the whole deposit, and consist of Radiolaria, Sponge spicules, and 
a few Diatoms. 
Fragment of White Chalk. — From 994 fathoms, off Nuevitas, Cuba, 
there was obtained a fragment of white chalk coated on the surface with 
streaks of peroxide of manganese. This chalk contained 90.24 per cent 
of carbonate of lime. The sections showed the rock to be composed of 
erystalline grains of carbonate of lime, which however were not the 
result of precipitation. A few sections of Globigerina and Textularia 
were observed, but no other organisms could be recognized. After dis- 
solving away a considerable quantity, small fragments of quartz and 
hornblende, Sponge spicules and Radiolarians were observed in the resi- 
due. It is impossible to be certain that this rock was formed in the 
position from which it was dredged, though there are reasons for sup- 
posing that it was. The ooze which came up from the same place was 
of a reddish or brownish tinge, and contained an immense number of 
Pteropods, Heteropods, and pelagic Foraminifera; the percentage of 
lime was not so high as in the white chalk rock, and the residue was 
much darker in color. 
Concretions. — Off the Barbadoes in 221 fathoms (St. 280) a very 
hard calcareous concretion was obtained, which showed perfectly how 
the rock was formed by crystallization of carbonate of lime around the 
shells of Foraminifera and other centres. A zone is seen around the 
shells, composed of fibro-radiate calcite; the crystals of calcite, coming 
from the various centres, abut against each other, and frequently leave 
