GEOLOGY: W. M. DAVIS 
197 
a = 4.74 X 10- 8 cm.; h = 6.65 X 10" 8 cm. 
dn2 0 = 3.79 X 10~ 8 cm.; c? 10 Io = 2.37 X 10~ 8 cm.; d 000l = 3.32 X 10~ 8 cm. 
The arrangement of the lattices is conveniently explained by referring the 
origin of each lattice to two unit axis making an angle of 120° and a third 
TABLE 6 
Values of K and Corresponding Approximate Values of x When h = 14.75 cm. 
INDEX 
4> 
Sin tf> 
MODEL I 
MODEL II 
MODEL III 
MODEL IV 
K 
X 
K 
X 
K 
X 
K 
X 
1011 
58°18'30" 
0.8509 
i 
2 
1.8 
r • 
0.9 
1 
0.9 
1 
0.9 
1012 
39° 9' 9" 
0.6293 
1 
1.2 
1 
1.2 
1 
1.2 
1 
1.2 
1013 
28°22' 0" 
0.4751 
1 
2 
3.1 
1 
1.6 
1 
1.6 
1 
1.6 
2021 
72°50'20" 
0.9555 
1 
4 
3.2 
i 
2 
1.6 
3.2 
1 
3 
2.4 
3031 
78°22'13" 
0.9795 
1 
6 
4.5 
1 
2.2 
4.5 
1 
6 
4.5 
3032 
67°37 , 36" 
0.9248 
1 
3 
2.6 
1 
3 
2.6 
2.6 
1 
3 
2.6 
3034 
50°32'15" 
0.7720 
1 
3 
2.9 
1 
3 
2.9 
2.9 
1 
3 
2.9 
4041 
81°13'30" 
0.9886 
1 
8 
6.6 
1 
2.2 
9 
3.3 
1 
4 
3.0 
mutually perpendicular to these. The coordinates of the origins are then 
0,0,0; if ,1/ss; if, }; 0,0, (z + 2)/2z. 
The values of z, that is the relative displacement of the two planes making 
up a basal pair, is uncertain and needs further investigation. This requires 
a careful determination of the. relative intensities of the spectra of different 
orders reflected from the 0001 planes and was beyond the scope of the present 
investigation. Conditions of symmetry suggest a value of z = 6, but this is 
purely conjectural. 
The investigation was pursued under the direction of Prof. A. G. Webster 
of Clark University in the Physics Laboratory of the Worcester Polytechnic 
Institute. 
1 Paris, C.-R. Acad., Set., 157, Nov. 17, 1913, (924-926). 
2 Dana, System of Mineralogy, 1888 ed., p. 205. 
FRINGING REEFS OF THE PHILIPPINE ISLANDS. 
By W. M. Davis 
Department of Geology and Geography, Harvard University 
Read before the Academy, April 23, 1918 
A series of large-scale charts recently published by the United States Coast 
and Geodetic Survey for certain parts of the Philippine islands are, apart 
from their value to commerce, of much scientific interest in connection with 
