JUNCTIONS OF OUR ROCKS. 31 
It may here be noted with regard to the primitive 
series of rocks, that they are nearly all observed to 
amalgamate with, or pass into one another, as well 
as into rocks of a more recent date, thus granite and 
slate are found sometimes blended, gneiss and gran- 
ite, mica-slate (allowing it to be primitive) and clay 
Slate, mica-slate and gneiss, trapp and slate, while 
porphyry is seen imbedded in slate, or in sandstone 
in some situations. 
Again, prior to entering on the subject of the 
next series, it may be as well to note, that the same 
kind of admixture prevails there also,—the various 
varieties of slate graduate one into another, as well 
as into the true greywacké rock, slate also, passes 
into lime, lime into dolomite, and sandstone into 
slate. 
But, it must be observed that while igneous 
causes might induce some of those amalgamations 
in the first class, contemporaneous precipitation, 
most probably induced the reciprocal series of ad- 
mixtures in the second, as I shall endeavour to 
shew in the sequel. Setting however all theory 
aside, the practical geologist will bear in mind, that, 
tracing the series of our rocks from the coast on- 
wards to the moor, he will encounter a consecutive 
admixture of various collateral strata in his course: 
thus,—slate and sandstone, slate and greywackeé, 
greywacké and sandstone, porphyry and sandstone, 
lime and sandstone, lime and dolomite, lime and 
slate, trapp and slate, porphyry and slate, clay-slate 
and mica-slate, granite and slate, besides some 
other combinations of minor consequence. In the 
rocks surrounding the E.ddystone, a combination of 
granite and gneiss occurs. ‘The Eddystone itself, 
iS gneiss. 
I desire to be understood, as speaking provision- 
ally on the general question of classification and 
eras, and as leaving it open at all points for ma- 
