Prof. J. Mitne—Distribution of Volcanos. “SF 
the character of which would appear in a great measure to be 
dependent upon the primary results by which they were preceded. 
Amongst the secondary results I would point to the position occupied 
by many volcanos. 
If we take a map which shows the distribution of voleanos upon 
the surface of the globe, we shall observe that the greater number of 
these are situated in the vicinity of the oceans, and of these the 
most extraordinary range are those which circumscribe the Pacific. 
In the Atlantic and Indian Oceans, if we except the group of 
mountains which build up Iceland, there are comparatively but few. 
This remarkable distribution of volcanic vents has been noticed by 
many writers, who, whilst speculating on its meaning, have offered 
theories for its Solution. To what has already been written, I now 
venture to offer a few additional notes. 
First, we must observe that the Pacific Ocean, as compared with 
other oceans, as, for instance, the Atlantic, appears to be the deepest 
tract of water which covers the face of our planet.! 
This would seem to indicate that the shores of the Pacific are 
steeper than those of the Atlantic; and that this is probably the case 
we can convince ourselves by examining the maps of a Physical 
atlas.’ 
If we do this, we shall see on the South American coast the Andes, 
some of the peaks of which are more than 20,000 feet in height, 
sloping down beneath a sea which is 12,000 feet in depth. 
Along the North American coast the slope is not so great, because 
the Rocky Mountains, which form the high ground, lie farther inland. 
In the Aleutians, the Kuriles, in Kamschatka, and in a great 
portion of Japan, the slopes are quite as great as they are in South 
America. In §. America the slope is great, because the mountains 
are high ; but in these latter districts it is because the neighbour- 
ing sea is deep. 
In Australia there is a very gentle slope. For the purpose of 
comparing together the various slopes we find upon the surface of 
the earth, I have drawn a large number of sections at right angles 
to coast-lines, each representing a length of 120 sea-miles, and 
having the same scales both vertically and horizontally, one end of 
these sections representing land beneath the sea, and the other end 
the land bordering on the coast. The following are a few of the 
slopes which I obtained upon various coasts. 
On the west coast of South America, from Aconcagua, which is 
about 24,000 feet high, down into the sea, which is 2,000 fathoms 
in depth, the slope is about 1 in 20-2, In a 8.E. direction, from 
1 According to Dr. O. Kriimmel, the average depth of the Pacific is 3887 metres, 
whilst the Atlantic is 3681 metres. 
2 If we consider the mean height of the land which bounds the Pacific, and com- 
pare it with the mean height of that which bounds the Atlantic, we shall be brought 
to a similar conclusion. Some idea of what their heights would be may be obtained 
from the mean heights of the several continents, which are as follows :— 
South America .. ... 1,182 feet. | BULOPC ses, sae, rene, ane 000 teRt 
North America... .. 748 feet. Africa sget can Wess) BZOUUL teebin 
Meas ws AR Me’ wee 1150 fects | Australia ... .. .. 600 feet? 
