Ji 
С) 
115 
therefore, a very interesting fact that the only dike of the 
coastal area conforming in direction with these joints is the one 
small example of the third system. 
East-west joints are also 
well developed in the coastal melaphyr ; but they have, with few 
exceptions, a decided southerly hade of 20° to 80° ; while the 
east-west dikes, almost without exception, are vertical or have 
a northerly hade, showing a tendency to be, as a rule, approxi 
mately normal to the bedding planes of the melaphyr, tuff, and 
conglomerate. 
East- West Dikes of the Central Belt. 
No. Trend. | Hade. 
20! Мег ДА Vert.-N.15' 
2L Nd d N. 159-20" 
49 NOTA" M Vert.-N. 8 
28 | N: 7109-809 E.] Vertical 
24 IN TO UN Se 
25 М. 809 E N. 20°-25 
n N. 5 
e N. 15 
98 | B, 80° R Vertical 
29 | S. 80° E Vert.-N.10' 
M, Т0” 2 N. 10 
S. 809 Е. N. 200-30 
S. 80° E N. 159-20 
m Td H N. 169-20* 
S. 759-809 E. | N. 409-50 
S. 75°-77° Е N. 109-15* 
86 | E.-W. N. 59-10 
The central belt extends 
Width 
| їп 
feet. 
| 6-8.5 
Remarks, 
North end of Rocky Neck. 
Probably a branch of 20. 
Probably faulted six times. 
Parallel with 22 on Rocky Neck 
Porphyritic. Parallel with 22. 
Porphyritie; a fault-dike. 
Cuts 25 on Melaphyr Plateau. 
Porphyritic; a fault-dike. 
Regular; and no apparent 
faults. 
Possibly not one continuous 
dike. 
An important fault-dike. 
Possibly a continuation of 84. 
Branch of 81. 
Probably a branch of 81. 
Double dike. 
Unrecognized west of the rail- 
rond. 
Branch of 35. 
from the shore of Strait’s Pond, near 
Folsom's Island, across Conglomerate and Melaphyr Plateaus, 
and thence along the south shore of Nantasket Harbor to Rocky 
g À 
Neck. 
Doth of the east-west systems are represented in this 
belt: but, as before, the second system largely predominates. 
Although the exposures are, as a. rule, less satisfactory than in 
the coastal belt, individual dikes can, in several instances, be 
