1881 .] 
289 
[Wadsworth. 
The felsite extends northward from the granite, and its band- 
ing dips seaward as is natural upon a shore flow of lava. Lying 
upon this, is to be found the remains of the trachytic lava which 
was poured over this felsite, then as now exposed to the action 
of the waves. 
Between the trachyte and underlying felsite there is to be 
found in many places a conglomerate of varying thickness of from 
one to six inches. This conglomerate is composed principally of 
a fine felsitic debris (1229) 1 holding angular and rounded frag- 
ments of the felsite. The matrix of the conglomerate is, from 
decomposition, a dirty yellowish white, clayey material. It is 
probable that this conglomerate was formed by the action of the 
waves upon the felsite, although a volcanic rhyolitic or trachytic 
ash would have a similar structure, if preserved under like condi- 
tions. In some places the trachyte rests directly on the felsite 
without any intervening material. The line of contact of the 
trachyte with the felsitic debris is well marked, and the former 
conforms to the irregularities of the latter (1222, 1225, 1226, 
1227, 1228). This is well seen when a specimen is obtained 
detached from the underlying conglomerate. The base of the 
trachyte then shows a very rough pitted and indented surface 
(1224, 1281, 1232). By digging it was found in one place that 
the trachyte filled a small basin-like depression, connected by a 
long shallow handle-like mass with a larger body of rock. 
The trachyte being exposed to the alternate action of the 
waves, sea water, sun, and rain, has suffered much therefrom, and 
in most places is decomposed or altered. The least altered 
portions obtained are of pale greenish, brownish, and purplish 
gray tints, with a compact groundmass, holding here and 
there a feldspar crystal. The color and somewhat crystalline 
structure of the fractured surface causes the rock to closely 
resemble some magnesian limestones. The groundmass under a 
lens is seen to be filled with minute ledge-formed feldspars. 
These crystals are arranged in lines showing fluidal structures. 
These fluidal lines correspond with the contours of the irregular 
line of contact with the felsitic debris, and are seen to bend 
1 The numbers refer to the numbers of the specimens in the Lithological Collection 
in the Museum of Comparative Zoology at Cambridge, Mass. 
PROCEEDINGS B. 3. N. H. VOL. XXI. 19 APRIL, 1882. 
