EXPLANATION OF PLATE 1. 
9 
the form of Dykes, filled with materials similar to those 
which form the masses that have overflowed in the Vici- 
nity of each Dyke.* 
Changes effected by the Igneous Rocks, on the Strata 
in contact with them. 
The peculiar condition of the rocks that form the side 
walls of Granitic Veins and Basaltic Dykes, afibrds ano- 
ther argument in favour of their igneous origin j thus 
wherever the early Slate rocks are intersected by Granitic 
Veins (a. 8.) they are usually altered to a state approxima- 
ting to that of fine-grained Mica-Slate, or Hornblende- 
Slate. 
The Secondary and Tertiary rocks also, when they are 
intersected by basaltic Dykes, have frequently undergone 
some change ; beds of Shale and Sandstone are indurated, 
and reduced to Jasper; compact Limestone and Chalk are 
converted to crystalline Marble, and Chalk-flints altered to 
a state like that resulting from heat in an artificial fur- 
nace.-j- 
In all these cases, the Phenomena appear to be through- 
out consistent with the theory of igneous Injection, and to 
he incapable of explanation on any other Hypothesis that 
has been proposed. A summary statement of the probable 
relations of the Granitic and Trappean Rocks to the other 
Materials of the Globe, and to one another, may be found 
in De la Beche’s Geological Researches, 1st Edit. Pag. 
374, et seq. 
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^ T 
■ ” dykes the materials have been variously modified, by 
eir mode of cooling, and differ from the masses which overflowed 
the surface. 
1" Examples of this kind occur on the sides of Basaltic Dykes in- 
®rsecting Chalk in the County of Antrim, and in the Island of 
hghlin. See Geol. Trans. London, O. S. vol. iii. p. 210. pi. lo. 
