188 THE ANTARCTIC MANUAL. 
XI. 
INSTRUCTIONS ON THE OBSERVATIONS 
WHICH SHOULD BE MADE IN CASE VOLCANOES OR 
EVIDENCES OF VOLCANIC ACTION SHOULD BE MET 
WITH. 
By J. W. Jupp, C.B. LL.D. F.RS. 
SHovLD any volcanic rocks be met with, the following suggestions 
may aid the observer in directing his attention to the most important 
points in connection with them. 
I. Zf the rocks have a fresh appearance, and are of comparatively 
recent origin, the following circumstances concerning them should be 
particularly noted :— 
A. Lava-STreams. Concerning these should be recorded— 
a. Dimensions. Distance from point of origin ; breadth at various 
parts of course; thickness, so far as it can be determined, and 
especially as affected by the accidents which the current meets with 
in its flow. 
b. Slope over which they flow. This should be measured at various 
points with a clinometer if possible, and, at points where the inclina- 
tion suddenly changes, any variations in the dimensions or other 
characters of the current should be carefully noted. 
c. Surfaces of lavas, Attention should be paid to the features 
presented by these, whether smooth and “ropy,” or bristling and 
scoriaceous. 
d. Texture. Note specially if the rock of the current be por- 
phyritic, compact, globular, concretionary, pumiceous, glassy, spheru- 
litic, or coarsely crystalline. If the rock presents ribboned or banded 
structures, observe, if possible, the relations of these to the direction 
of flow of the stream. When the rock exhibits transitions from one 
texture to another, collect series of specimens, illustrating the grada- 
tion. Note especially changes between the surface and interior of 
eurrent, or those taking place at different points of its course. 
