Ch. II.] 
TRANSITION FORMATIONS. 
13 
respecting the nature of granite. First it was shown, by nume- 
rous examples, that ordinary volcanic dikes might produce great 
alterations in the sedimentary strata which they traversed, caus- 
ing them to assume a more crystalline texture, and obliterating 
all traces of organic remains, without, at the same time, destroy- 
ing either the lines of stratification, or even those which mark the 
division into laminae. It was also found, that granite dikes and 
veins produced analogous, though somewhat different changes ; 
and hence it was suggested as highly probable, that the effects to 
which small veins gave rise, to the distance of a few yards, might 
be superinduced on a much grander scale where immense masses 
of fused rock, intensely heated for ages, came in contact at great 
depths from the surface with sedimentary formations. The slow 
action of heat in such cases, it was thought, might occasion a state 
of semi-fusion, so. that, on the cooling down of the masses, the 
different materials might be re-arranged in new forms, according 
to their chemical affinities, and all traces of organic remains might 
disappear, while the stratiform and lamellar texture remained. 
May be of different ages. According to these views, the 
primary strata may have assumed their crystalline structure at 
as many successive periods as there have been distinct eras of 
the formation of granite, and their difference of mineral com- 
position may be attributed, not to an original difference of the 
conditions under which they were deposited at the surface, but 
to subsequent modifications superinduced by heat at great 
depths below the surface. 
The strict propriety of the term primitive, as applied to gra- 
nite and to the granitiform and associated rocks, thus became 
questionable, and the term primary was very generally sub- 
stituted, as simply expressing the fact, that the crystalline 
rocks, as a mass, were older than the secondary, or those which 
are unequivocally of a mechanical origin and contain organic 
remains. 
Transition formations. The reader may readily conceive, 
even from the hasty sketch which we have thus given of the 
supposed origin of the stratified primary rocks, that they may 
