A. Somervail—The Lizard Greenstone. 495 
the fine sediments having been dropped by floating-ice also well 
accounts for the deposition of the boulders without much water-wear. 
This was the theory suggested by Dr. Blanford many years ago, and 
on the whole is the most probable of any of the theories suggested. 
It may be that these boulders were not all transported in the same 
manner. The clays and sands that were formed off the shore of the 
sea in Maine during the “Champlain” elevation of the sea are 
strewn with erratic boulders up to twenty feet in diameter. The 
clays are fossiliferous and must have been formed in the open sea. 
The boulders were dropped from floes of shore-ice or small bergs. 
Every winter the shore-ice becomes attached to boulders, and in the 
spring these boulders are carried out to sea and along the coast when 
the ice becomes detached from the shore. This hypothesis therefore 
_ postulates a process that is known by actual observation to be an 
efficient one. 
It is not the writer’s purpose, however, to enter on the general 
question. The character of the specimens imperatively demands 
some method of transportation that did not involve much water-wear 
and permitted the preservation of the scratches on the surface. 
But the specimens afford little evidence as to the exact manner of 
their transportation. 
Cotorapo CoLLeGE, Cotorapo Sprines, U.S.A. 
X.—On THE GREENSTONE aND AssocraTED Rocks oF THE MANACLE 
Point, Lizarp. 
By ALEXANDER SOMERYVAIL. 
N De La Beche’s Geological Survey Map of Cornwall are three 
colours representing the associated rocks at, and on each side 
of the Manacle Point. The Point itself and for a considerable distance 
south of it is represented as a greenstone. Partially encased in the 
greenstone and to the south of it is gabbro, which forms the main 
mass of this rock in the Lizard district. On the north side of the 
greenstone which forms the extreme south wall of Porthonstock 
Cove is hornblende-schist, which with some serpentine and other 
rocks terminates against the killas, or slates near Porthalla. 
Several observers with seeming good reason have drawn attention 
to the fact that the greenstone as represented on the map is made to 
cover much too large an area to the south, and that any one walking 
from this direction, or the reverse, finds gabbro where the former 
rock was expected to occur. That this is the case, there is absolutely 
no doubt, but, De La Beche may have had his own reasons for this, 
although perhaps not distinctly stated in the text of his accom- 
panying memoir. 
Not only does this seeming discrepancy exist with regard to the 
relative extent of these rocks, but one also soon seems to get involved 
in another with regard to their relative ages. 
It has been taken for granted somehow or other that the green- 
stone is the newer rock, as it seems to cut the gabbro; but at 
Porthonstock this is entirely reversed, the gabbro in several instances 
traversing the greenstone. 
