174 Proceedings of the Cmnhidge Philosophical Society. 
(3.) That it is interlaced with the other strata, in such a way 
as cannot be accounted for by any h 3 ’pothesis of tranquil deposi- 
tion, and subsequent dislocation. 
(4.) That the strata in contact with the trap are always chan- 
ged. The limestone, under such circumstances, is partially con- 
verted into a mass as white as statuary marble, in which the 
impressions of shells are entirely effaced. At greater distances 
from the trap the change is partial. The shale, under like cir- 
cumstances, undergoes many remarkable changes. In some 
places it is constructed into a hard porcellanous mass. In others 
it puts on a slaggy cellular appearance, and the cavities are of- 
ten studded with minute garnets, &c. &c. 
From all these facts, the author concludes, 
That the great faults in Teesdale have originated in the 
operation of causes, similar to those which have produced those 
dislocations in the coal measures which are described in a pre- 
vious paper. 
^dy That the whin of Teesdale originated in the same system 
of causes which produced (though perhaps not contemporane- 
ously), the great whin-dikes in the coal measures of the same 
district. 
March 17. — Professor Sedgwick concluded the reading of his 
paper. 
T. E. Bowdich, Esq. forwarded to the Society a Botani- 
cal description of Madeira. In this communication Mr Bow- 
dich has given a list (including S77 genera), containing the 
indigenous, naturalized, and cultivated plants, found in Ma- 
deira. Of the indigenous plants, be has detected 149 genera. 
He describes their geographic distribution, and concludes his 
paper with an enumeration of 17 new genera, 10 of which are 
among the Cryptogamous, and 7 among the Phasnerogamous 
plants of the island. 
April 14. — W. Whewell, M. A., Fellow of Trinity College, 
read a historical notice on the attempts which have been made 
to grind optical glasses and mirrors by machinery, and to give a 
parabolic form to them. 
Rev. G. Peacock, M. A., F. R. S., Tutor of Trinity, com- 
menced a paper upon some points of mathematics connected with 
the Newtonian discoveries. 
