224 The Philippine Journal of Sctence 1921 
firm dealing in a patent type of concrete construction, that none 
of its buildings had suffered any damage at the time, were 
strictly correct, for no buildings in Manila were damaged! 
Another instance in which vulcanism did play an important 
_ part was that in which a section of road in Albay Province, 
Luzon, was obliterated for a distance of 83 to 5 kilometers 
by a fall of bombs and a deluge of mud and ashes from Mayon 
Voleano in 1915. As volcanic activity in the Recent period in 
the Philippines has been entirely of the explosive type in which 
no lava outpourings occurred comparable to those from the 
Hawaiian volcanoes, the damage resulting to public works would 
be of very different character and also less serious. 
Gradation.—This is the sum total of the wearing-down pro- 
cess, in many respects the dominant type of geological work. 
If we analyze this process we find that the following agents 
are contributory: a, weathering; 0, transportation ; c, corrosion ; 
d, corrasion. I would, however, make “corrosion” a subheading 
under weathering, there being two factors involved; namely, 
a mechanical deformation and a chemical change, either of 
which may precede the other. Once weathering, or to use a 
very crude term defining it in part only, “slacking,” has taken 
‘place, transportation comes in and does its work; and then 
“eorrasion,’ or mechanical wear, becomes operative, but not 
until there is movement. 
Of course, these factors are operative in all countries and 
under nearly all conditions, but gradation proceeds at a maximum 
rate in the Tropics. Two reasons are given for this; namely, 
rainfall and temperature or, in a word, climate. 
In the Philippines we have a mean annual rainfall of well over 
2,540 millimeters (100 inches), with sometimes exceptional and 
almost unprecedented precipitation, notably 1,168.1 millimeters 
(46 inches) in twenty-four hours on July 29, 1911, at the Ba- 
guio Observatory. This is, as far as we know, the world’s record 
for a single rainfall. The reported rainfall of 23,387 millimeters 
(905 inches) a year at Cherraponji, in Assam, has lately been 
questioned. However, a precipitation of over 15,240 millimeters 
(600 inches) has been recorded on Mount Waialeale, Kauai Is- 
land, H. T. At such times the streams leave their banks and 
spread out over the country in sheets of water. Needless to say, 
the amount of material then transported is almost unbelievable. 
Furthermore, we have another factor to consider, and that is 
velocity. Often this is not taken into consideration. When we 
stop to consider that doubling the velocity of a stream means 
