18,3 Smith: Tropical Geology and Engineering 223 
and the Philippines. Once before, and perhaps twice, the bar- 
rier of the Isthmus of Panama, which has cost so much in life, 
labor, and money to cut through, has been opened so that the 
waters of the Atlantic and the Pacific intermingled, and it is 
not at all impossible that future diastrophism will render all 
our labor useless. However, these movements are so slow as to 
be almost negligible in any one generation. Only the geodesist 
finds that he has to readjust some of his calculations. We see 
the results in many parts of the world of such movements, but 
as yet we do not know much about them. Our data are not 
sufficient. Two facts are established, however; namely, that 
such movements as have taken place in the Philippines have 
been great during the late geological periods, amounting to as 
much as 1,800 meters, and that they have been differential. 
There has been within the Recent period a marked tilting of the 
Philippine block toward the Pacific Ocean. This will explain to 
the engineer why we have comparatively shallow river mouths 
on the west side of the Archipelago, and deep, drowned ones 
on the eastern side. It should be stated that in some parts of 
the Archipelago, notably Cebu, the reverse is the case, which 
further substantiates the statement, 
Vulcanism . — As the Philippine Archipelago is a part of the 
so-called “Circle of Fire” that girts the Pacific Ocean, we natur- 
ally expect vulcanism to be of such magnitude that engineers 
would be continually anxious. Nevertheless, except for those 
regions in the immediate vicinity of active volcanoes, little 
damage has ever been recorded from this cause. The most- 
marked effects were those noted in 1911 resulting from the 
explosive eruption of Taal Volcano, situated about 45 kilometers 
due south of Manila. Had there been a large city (the size 
of Kingston, Jamaica, for example) situated on the shores of 
Lake Bombon, tremendously greater loss of life and damage 
might have occurred. The town of Taal, a few kilometers 
distant, suffered to the extent that an old church made of 
volcanic tuff was badly disfigured and a triangular sec- 
tion of land, crossed by one of the Government’s new 
highways, dropped about a meter, allowing the tide to 
come inland for perhaps four-fifths of a kilometer. The length 
of damaged road amounted to about 3 kilometers. These 
effects were due directly to earthquakes and indirectly to the 
volcano. Although four hundred ninety-eight distinct shocks 
were recorded in Manila at the time of the eruption, practically 
no damage there was noted. The claims of a certain American 
