140 C. A. SUSSMILCH. 
- 
V. THE VOLCANIC SERIES. 
It is not intended to give any detailed description of 
these rocks in this note. They form portion of the immense 
accumulation of lavas and tuffs which go to form the group 
of extinct volcanic peaks known as the Canoblas mountains. 
They consist, in the area mapped, mainly of basalt flows, 
but andesites, and andesitic and trachytic tuffs also occur, 
particularly towards the Canoblas. These deposits are 
everywhere unconformable with the underlying Silurian 
and Devonian strata, and are most probably of Tertiary 
age. 
VI. SUMMARY. 
The nature of the Silurian sediments indicates tranquil 
deposition in an open, comparatively shallow sea, consider- 
ably removed from any shore line, and accompanied by a 
slow, intermittent subsidence. Towards the close of the 
period vulcanism became an important feature, as evidenced 
in the thick beds of tuff and rhyolite. 
The Devonian sediments, on the other hand, indicate 
shallow water conditions of deposition, with dry land in the 
immediate vicinity to provide the coarse sediments of which 
most of the strata are composed. 
With the close of the Silurian Period, a deformative 
movement, perhaps already heralded by the pronounced 
vulcanism, began to affect the earth’s crust, resulting 
probably from the stresses in the earth’s body accumulated 
during the long continued sedimentation which marked the 
Silurian period. This resulted in the elevation of portion, 
at least, of the Silurian sediments into dry land, with the 
initiation of a new cycle of erosion. This deformative 
movement probably continued more or less throughout the 
Devonian period, and culminated in the great mountain 
building of the Carboniferous period, when all the Silurian 
and Devonian strata were folded into a great series of 
