XIV, 6 Dar Juan and Elicano: Philippine Glass Materials 467 
tion of some Philippine limestones. The analyses given in 
Table II show that they are almost pure. 
Table II . — Analyses of some Philippine limestones. 
[Numbers give percentages.] 
Constituent. 
Cebu. 
Binango- 
nan, Ri- 
zal, 1912 a 
Binango- 
nan, Ri- 
zal, 1918. 
Montal- 
ban, Ri- 
zal, 1912 a 
Montal- 
ban, Ri- 
zal, 1918. 
Palsaba- 
ngan, Ta- 
yabas. t 
43.45 
43.31 
43.49 
43.04 
43. 98 
43.48 
Silica (SiOa) 
0. 86 
1. 12 
0 . 88 
0. 94 
0.26 
0.69 
Iron and aluminium oxides (R 2 O 3 ) -- 
0.23 
0. 15 
0. 48 
1. 14 
0.09 
0.35 
Lime (CaO) 
64. 67 
63.78 
54.39 
54.61 
54.97 
64.68 
Magnesia (MgO) 
0.46 
1. 19 
0.68 
0. 22 
0.72 
0. 48 
0. 77 
0. 66 
• Analyzed by Forest B. Beyer. Analyzed by F. D. Reyes, chemist, Bureau of Science. 
SILICA 
The principal source of silica is white sand or quartz. Sand 
deposits of good quality occur at Paracale, Camarines Province, 
and in the Mountain Province at Baguio; but the deposits of 
commercial importance are the extensive beaches of quartzose 
sand and the vein-quartz gravel and bowlders found in Lubang 
Island, Mindoro. 
The quartzose sand is the result of the disintegration of the 
intrusive granite that outcrops on the narrow isthmus at the 
south end of the island, between Looc and Tabahin Bays. This 
sand is composed mainly of quartz, orthoclase, and mica, with 
variable proportions of clay. 
The sand deposits are found along the southern shore of Looc 
Bay, from the barrio of the same name to Balacbalac Point, and 
along the shores of Tabahin Bay, which lies between Caybanac 
and Natulo Points. Each of these extends both above and be- 
low the present beach and together make an area of about 2.5 
square kilometers. Between the high- and the low-water marks 
the sand is subjected to the constant action of the waves, with the 
result that a gradual concentration takes place, leaving a product 
of almost pure quartz. The width of the area containing the 
clean quartz sand averages 2.5 meters, extending throughout 
the length of both the Looc and Tabahin shores. From the 
high-water mark to the foot of the hills, which apparently at 
one time was a water level, the sand is mixed with greater or 
less quantities of clay. Below the low-water mark the sand ex- 
tends into the sea about 200 meters. The probable thickness 
