156 TRANSACTIONS OF THE PLYMOUTH INSTITUTION. 
We at once dismiss, with Sir Warington Smyth, "the old 
Wernerian idea, that" the associated "schists were deposited after 
the solidification of the granite, wrapping smoothly round it." 
Indeed, that notion had to be abandoned with the exploded 
hypothesis of the primary granitic character. 
As an igneous rock, the Dartmoor granite might have been 
intruded in four ways. 
A. It might have risen directly through the Devonian and 
Carboniferous strata, bearing up on its surface the displaced rocks 
of its area. But in that case, its boundaries must have been 
broken or "fault" boundaries, and the fractured ends of the 
surrounding rocks must have terminated abruptly against it, 
instead of being tilted with it and lying partially upon it. 
B. It might have elevated the superincumbent mass in a huge 
unbroken dome. But in that case, the removal of the upper 
portion of this dome would have shown the lowest rocks, in all 
cases, next the granite ; whereas it is seen to pass under Devonian 
slates on the south, and under Carboniferous slates and grits on 
the north. 
C. To avoid these difficulties, Mr. Ussher, f.g.s., recently 
suggested a laccolitic origin. His hypothesis was, that the granite 
came up from below through a central channel, and then forced 
itself in all directions between the beds and along lines of 
weakness under the surface, the final form being comparable to 
that of a gigantic mushroom. This would fully account for the 
relations of the granite to the investing rocks, but is, I think, 
inadmissable for other reasons. First. We cannot treat the 
Dartmoor granite as an isolated fact; hence, instead of one 
laccolite, we should have to accept several. Second. On the 
laccolite view there must be stratified rocks, except at the neck, 
below the granite as well as above, and in sinking through the 
granite we should come upon them. This is contrary to all 
experience. In the Cornish mines the lodes are continually 
followed down from the killas irito*the granite, and the two rocks 
invariably meet at an angle, as if the slate were lying in a huge 
granitic lap. But when the granite is once reached, there is no 
return to the killas, with the single exception that in the Breage 
district the rule is proved by the granite being cut in veins 
protruded into the killas. Third. It is impossible to me to 
conceive of such an immense body of molten matter as a laccolite 
