W. M. Hutchings— Altered Igneous Rocks, Tintagel. 53 
extent being limited to the difference between the measurement of the 
portion of the earth’s circumference and the Chord of its Are included 
in any area referred to. This variation will be found comparatively 
so slight as to be utterly inadequate to account for the presence of 
such foldings as occur in many districts; though it is to such a 
cause they are not infrequently attributed. The impossibility of 
these contortions being the result of such subsidence may be best 
illustrated by taking two slips of wood (Fig. 1 a, 6) of equal length 
—say 10 feet—fastened together at one end by a hinge (c) ; one (a) 
being fixed so as to remain straight, the other (b) bent to represent 
a curve, the greatest distance (d) between the chord (a) and the 
curve (b) being six inches; it will be apparent that the distance 
between the extremities of the slips of wood will be very slightly 
over three-quarters of an inch (e) ; an amount too insignificant to be 
ae eee 
capable by the pressing down of the one upon the other to form 
foldings such as are frequently met with in geological formations. 
(To be continued.) 
IJ.—Nores on Autrerep Ienrous Rocks or Tintacen, Norra 
CoRNWALL. 
By W. Maynarp Hurcuines, Esq. 
hee the autumn of 1887, during a stay in North Cornwall, I paid 
ia hasty visit to Tintagel, and took away a few specimens of 
rocks, without, however, having time or opportunity to examine 
more than very superficially into their field-relationships. 
In subsequently studying sections with the microscope I found 
myself unable to correctly interpret some of them, notably a certain 
highly schistose rock consisting mainly of calcite and chlorite, with 
residues of triclinic felspars. Mr. Teall, who very kindly looked 
over several sections for me, suggested that this was a highly 
altered and mechanically metamorphosed igneous rock, which might 
prove to be derived from a certain epidiorite occurring not far from 
it; and made other remarks and suggestions which decided me to 
pay another and longer visit to Tintagel in the following year. 
_As a result of this visit, and the subsequent examination of a 
series of rock-specimens then collected, I venture to offer a few 
notes on the altered igneous rocks of the coast in the immediate 
vicinity, viz. from a point near Boscastle to the south end of 
Trebarwith Strand. 
The more or less altered ‘“Greenstones” of the coast further 
south have been studied and described to a considerable extent. A 
résumé of the work done is given and discussed in Teall’s “ British 
Petrography.” So far as I am aware, the corresponding rocks of 
