SHALER: EXPULSION OF GASES. 
99 
lation is clearly very variable, the evidence from the thickness of 
deposits of Palaeozoic age which are displayed in many parts of the 
world and which appear to have been formed in tolerably deep water 
leads us to suppose that the deposition may in places be going on with 
considerable rapidity. As this opinion as to the rapidity of deposition 
on the deep sea floors is contrary to that of other enquirers, I may 
venture to note one point which seems to me to throw some light on 
the matter. 
In the Java district there is a group of volcanoes, some half a dozen 
in number, which are characterized by a high order of energy; the 
explosions of these craters during the last century and a quarter have 
cast forth a mass of pumice and dust which cannot well be reckoned 
at less than one hundred and twenty-five cubic miles. Practically 
the whole of this material has gone into the sea, either falling directly 
into it or being swept there by the rivers. Thus in this outlet 
the contribution of materials which eventually find their way 
to the sea floor amounts at the present time to not less than 
a cubic mile per annum or somewhere about twenty times the 
annual contribution of the Mississippi River. It is likely that 
the total annual influx of volcanic matter to the sea floor is 
many times as great as that which comes from the Malayan 
group of vents. Reckoning the contributions from submarine volca¬ 
noes whose summits do not attain the ocean level, it may be that the 
total mass of such ejections which enter the growing strata exceeds 
on the average one hundred miles each year; moreover this rock 
debris from its generally vesicular nature floats for a long time before 
it finds its way to the bottom and may be to a great extent converted 
into very freely divided matter before it comes to rest, and in that 
state may give no distinct evidence of its volcanic origin. To this 
volcanic sediment we may owe a large part of the growth of marine 
dejmsits formed at a distance from the shore. Its distribution is 
doubtless very irregular, being to a great extent determined by the 
courses of the ocean currents; in large part it probably comes to rest 
in the field of ocean floors near to the points of extrusion. Studies 
which I have recently made on the compositions of the materials on 
our beaches have shown me that a certain portion of this matter along 
the shores of the United States is derived from bits of pumice which 
floated in the ocean waters and are driven against these shores, there 
to be ground up by the waves. 
Assuming: that from the contributions of volcanoes combined with 
