Dr. C. S. Du R. Preller—Ooast-Section at the Lizard. 221 
V.—NorTe on A Coast-Section AT THE LizarD. 
By C. 8. Du Ricur Preiser, M.A., Ph.D., Assoc.M.J.C.E., F.C.S., F.G.S. 
Ne the meeting of the Geological Society on February 8th, Mr. 
Teall exhibited, as one of the illustrations of his paper “ On 
some Coast-Sections at the Lizard,” an eminently characteristic and 
instructive diagram of serpentine and granite in juxtaposition ; and 
the interesting question whether the granite was intrusive in the 
Serpentine or vice versa, was ventilated and discussed, but by no 
means decided. 
From the accompanying sketch of the salient features of that 
section, it will be seen that the granitic mass, having the shape of 
an irregular inverted pear in longitudinal section, broad at the base, 
and gradually narrowing towards the upper end, is flanked on both 
et AS 
a 
Boe 
Serpentine. Granite. Serpentine. 
sides by the serpentine which, at one point, on the right side, pro- 
jects into the granite in the shape of a tongue. In the opinion of 
some, this last-named phenonenon seemed to lend weight to the 
conjecture that the serpentine was intrusive in the granite, in which 
case it would, of course, be younger than the latter. But, in my 
opinion, that very phenomenon affords conclusive proof of the con- 
trary being the case; for the tongue-shaped projection is only an 
indication that, at this particular point, the serpentine offered to the 
intrusive granite greater resistance than at other points of the section, 
that greater resistance being due to the more advanced state of 
solidification of the serpentine at that point when the granite erupted. 
This view appears further strengthened by the fact of the axis of 
the tongue pointing obliquely downward, in the teeth as it were, of 
the upward flow of the intrusive granite, which forced back the more 
yielding, viz. more or less plastic part of the serpentine, and left the 
already solidified nucleus in the form shown in the diagram. More- 
over, to the sharp inward curve of the granitic contact line produced 
by the serpentine tongue on the right, corresponds an outward curve 
on the left or opposite side, and the section thus exhibits the ordinary 
physical conditions of flow, the axis of the granitic complex being, 
on the whole, a flat curve, determined by the lateral resistance 
which that mass encountered in forcing its way upwards. The 
evidently more or less plastic condition of the serpentine at the 
time of the granitic intrusion also tends to show that the eruption 
