CHAPTER II. 
Basaltic Rocks, Dykes, Mineral Veins, Syc. 
Only one case of interposed pyrogenous rock occurs in the limestone 
tract of England to the north of Derbyshire, but this is one of the 
most extensive examples known in geology, and has given rise to 
several descriptions. Professor Sedgwick and Mr. Hutton, in particular 
have examined this rock with much attention and published different 
views concerning it. 
The toadstone of Derbyshire, whether it be a single or triple mass 
may be considered as one great eruption of melted rock interpolated 
in the limestone series ; the ‘ Whin sill,’ as it is called, of Yorkshire 
Durham, and Northumberland, is another. They do not correspond 
in position among the strata; the toadstone lies among lower beds 
than the Whin sill. They agree in some respects; both being to a 
certain extent stratiform, irregular in thickness, variously traversed bv 
faults and veins. y 
The Whin sill is a great mass of greenstone and basalt, extending 
from near Brough in Westmoreland to the northern parts of Northum- 
berland, occupying a position more or less definite immediately below 
or in the lower parts of the Yoredale series, never passing downwards 
to the Melmerby limestone, nor upwards to the main or twelve fathom 
limestone. In thickness it varies extremely, and within a small compass • 
there is generally but one stratiform mass; sometimes two, perhaps’ 
three, occur, (as near Bavington, Northumberland.) It has never been 
seen to pass into any of the numerous fissures of the limestone series, 
nor to send veins into their substance, but it occasionally includes 
