56 WARREN D. SMITH 
surface of the water—they naturally present, when elevated, a 
more or less flat platform upon which the rivers deposit their loads 
and in that way build up new land. On the east coast, it is not so 
easy to see this growth, as throughout much of its extent, the coast 
is sinking: witness the drowned river-mouths of the Paracale and 
other important rivers. 
The Pyroclastics—The present eruptions and those of the 
Pleistocene have generally been marked by great quantities of ash 
and rarely by out-pourings of lava. A great deal of this material 
happened to fall into the sea or other bodies of water and was 
subjected to a sorting process and as a result, we get the great beds 
of tuff so well developed adjacent to Manila. These beds alternate 
with marine sands showing rapidly changing conditions. 
This tuff has been experimented with and found to be of practical 
value in the making of a variety of sandlime brick. 
The greatest development of this, as has already been men- 
tioned, is around Laguna de Bay, near Manila. 
Placers.—On the east coast of Luzon in the vicinity of Paracale, 
Ambos Camarines, there is a considerable development of rich 
placer ground. The country is notable for the great number of 
‘stringers,’ rich in gold, most of which are too small to work on an 
extensive scale, but where they have been eroded and the detritus 
has become concentrated in pockets in some of the “drowned,” 
valleys on that coast, some remarkably rich ground has resulted. 
Gold and native copper as well as galena and sphalerite are found 
in them. 
In the streams near Manila, principally the Mariquina, some 
platinum has been found. Along the Bued River also are promis- 
ing placers. 
Laterite, etc—Naturally the action of weathering in the tropics 
is very important and very pronounced, but on the higher lands, it 
is not always so evident, because the tremendous rainfall quickly 
removes any unusual accumulation of material. 
The great development of ferro-magnesian minerals in the 
igneous rocks, results in an extensive accumulation of iron rich soil 
on the lower slopes, and this is so often like the deposit known 
as laterite, as to merit special mention as a distinct formation. 
