PLATE IV. 
Fig. 1. External form ami appearance of a typical nodule from the North Pacific (natural size). The little 
knob on the top is a small piece of pumice cemented to the nodule by enveloping layers of man- 
ganese, and the swellings on the side have a similar structure and origin. The nodules from 
this station looked like a lot of potatoes when rolled out of the dredge. Station 252; 2740 fathoms. 
North Pacific. 
Fig. 2. Typical manganese nodule from the Central Pacific (natural size). All the nodules taken at this 
station (about one hundred) have the same general form, and are the most compact of all the 
nodules dredged during the cruise. The upper surface is smooth, and very different in aspect 
from the under surface, which is covered with little rough mammillae, having spaces between them, 
giving this face a scoriaceous aspect. The whole nodule has a discoidal form. Station 274 ; 27 50 
fathoms, hlid Pacific. 
Fig. 3. One of several large slabs dredged among the nodules from the South Pacific, in section, and showing 
part of the upper surface (natural size). About the middle of the section there is a dark line 
which appears to represent the upper surface of an old sea-bottom, with manganese nodules 
imbedded or partially imbedded in the clay. A fall of ashes would appear to have taken place, 
covering the floor of the ocean in some places to the depth of an inch. The coarser particles lie 
immediately on the clay, and contain much black mica, then follow layers of finer and finer 
particles. Subsequently the bottom was apparently, after consolidation, rent by cracks, and layers 
of manganese were deposited over the upper surface and down the cracks, binding the whole into 
a compact mass. Station 281 ; 2385 fathoms. South Pacific. (For microscopical description of 
this slab see Plate XXI. fig. 2). 
Fig. 4. Round nodule from the same station, in section (natural size). On one side there is a whitish layer of 
volcanic ashes, over which, as in the case of the slabs, there is a layer of manganese. The side 
vith the layer of ashes had evidently been the upper surface of the nodule when resting on the 
bottom of the sea. Station 281 ; 2385 fathoms. South Pacific. 
Fig. 5. .^Vnother nodule from the same station (natural size), broken to show the Carcharodon tooth in the 
centre. Station 281 ; 2385 fathoms. South Pacific. 
Fig. 6. Upper surface of rather rare and irregular form of nodule from the South Pacific (natural size). It is 
more or less flattened, and j)resents a scoriaceous aspect, with a rugged appearance on the upper 
surface. The interior contains a yellowish earthy matter. Station 276; 2350 fathoms. South 
Pacific. 
Fig. 7. Section of another nodule from the same station (natural size). The interior does not present any con- 
centric stnicture, but there is an outer zone of concentric layers from 2 to 3 mm. in diameter. 
The nucleus was probably originally a piece of pumice. Station 276 ; 2350 fathoms. South 
I'ocific. 
Fig. 8. External surface of the same no^lulc (natural size), showing the scaly structure of the outer zones. 
