230 The Philippine Journal of Science 1921 
Maintenance on a road constructed of poor materials is one 
thing, while that on a road wherein a wise selection of metal 
has been the rule is an entirely different thing. In this a geolo- 
gist with his microscope is a necessity. Petrography, once 
looked upon as a mere academic study, is now indispensable to the 
scientific road builder. There is a pathology of rock just as there 
is a pathology of animal tissue. The microscope will reveal at 
once, and at little expense, whether or not the minerals com- 
posing the rock are sound, whether there is incipient decom- 
position, or a far-gone state of decay. It will show also the 
texture or fabric of the rock. If the rock has an ophitic texture, 
that is, the minerals interlaced to make up a sort of mat, then 
we may look for toughness. Why one rock splinters and 
another does not is at once made clear. 
At one time the writer collected rock specimens from a number 
of places along one of the principal Philippine highways, and 
among the samples was one that yielded a briquet which when 
placed in the Page cementation machine did not break under 
two thousands blows, whereas an ordinary basalt briquet yielded 
at the twenty-second blow. A thin section of the fresh 
rock was made and examination showed that there was a small 
amount of secondary calcite in the rock, an alteration product 
of the lime-bearing silicates; it was this that furnished the ex- 
cellent binding qualities. The rock was a diorite just begin- 
ning to decompose without having gone so far as to reveal this 
condition to the naked eye. This rock, with its holocrystalline 
texture and just the right amount of calcite, would make a most 
excellent road metal because it has two essential qualities, name- 
ly, toughness and high cementation quality. Of course, the 
objection of high cost will be raised at once; but no matter how 
the finances stand, there is never any excuse for putting worth- 
Jess and unsuitable rock on a road. The proper way is to let 
the geologist recommend one or more kinds of material, and 
then the engineer may consider which he can afford to use. 
Many state highway departments now follcw this method, and 
formerly the engineers of the Philippine Government always 
submitted their road and building materials to the Bureau of 
Science for the proper tests. Of late years this has not been 
done, and the results are beginning to appear. 
Still another important factor to be considered in connection © 
with the cementation quality of the road metal is that of the 
wind. During a typhoon, a storm which is much like the Gulf 
hurricane, the velocity of the wind is as high as 165 kilometers 
