Proceedings qfthe Cambridge Philosophical Society. 173 
proposes calling it, Electro-Dynamics. The object of these in- 
vestigations was to compare the results of this theory with that 
of Mr Barlow, and with experiment ; but they will require fur- 
ther development before they can be considered as sufficiently 
complete. 
A paper was read by Professor Sedgwick, M. A., F. B. S., 
Fellow of Trinity College, On the Association of Trap-Roch'., 
with the Mountain Limestone Formation in High Teesdalef 
&c. — The author commences with some general remarks on the 
structure of the great calcareous chain in the north of England. 
He then shews the great importance of the transverse valleys ; 
the upper and lower portions of which often exhibit a double 
system of sections, by which the relation of the formations are 
completely ascertained. He afterwards proceeds to examine the 
structure of the Higher Teesdale, and explains at considerable 
length the modifications which have arisen from the existence of 
many faidts of extraordinary length and magnitude. In this 
part of the paper, he first shews the want of correspondence in 
the strata on the two sides of the valley, which extends 5 or 6 
miles above Egglestone ; more especially the appearance of a 
great bed of trap on the south-west side, to which no bed cor- 
responds on the north-east side. 
2. He describes the phenomena exhibited by the trap after 
its first appearance in the bed of the river, till it crosses in the 
form of a great dam at the High Forse. 
3. He describes the appearance of a great fault, which inter- 
sects the whole valley about a mile above the High Forse, and 
throws the whole system of strata, on the north-west side of its 
range, more than 20 fathoms above their previous level. In 
the latter part of the paper, the author proceeds to examine the 
phenomena presented at the junction of the trap with the other 
strata, and he arrives at the following conclusions. 
(1.) That the great mass of trap (the whin-sill), may be traced 
to a point within a few hundred feet of the mass of trap, which 
is prolonged into the coal measures in the form of a dike. 
(2,) That the whin-sill is not a regular bed, but a great wedge- 
shaped mass, which becomes thickest in the upper part of the 
