LOWEST SILURIAN ROCKS FORMED FROM PRE-EXISTING GNEISS. 16* 
Here, at least, there can be no ambiguity ; for the whole of the adjacent low 
tract is composed of rolling hillocks of granite or granitic gneiss, which assume 
ac tly that appearance of bell-shaped masses, so happily illustrated by M. von 
’ and which we have endeavoured to represent in the preceding woodcut, 
one spot, we tiaced the granitic gneiss to within a few yards of certain quarries 
ittle above it which have been largely worked for millstones. The upper beds, 
witl^ S ^ n ^ Sant ^ ones ^ lose to which we have previously alluded, alternate 
gteenish-grey shale ; but in passing downwards they become a hard, dark- 
st ' ' ^ err r Ub ' nous and siliceous grit, beneath which is the band worked for mill- 
s ones. The latter (a' of the preceding woodcut) is, in truth, nothing but a pink- 
^ red, lecomposed gianite or granitic gneiss, in which the felspar and quartz are 
aggiegated into a mass completely resembling the Arkose of Brongniart. Though 
ere evidently constituting the true base of the Silurian system, this rock, resting 
°n t ie granitic gneiss of Sweden, could scarcely be distinguished in mineral cha- 
racters from an Arkose of tertiary age in Central France, which we saw many 
years ago ; so essentially do sedimentary rocks of different age resemble each 
other when constructed out of similar crystalline materials*. (See Lyell and 
Murchison, Ann. des Sciences Naturelles, Oct. 1629.) 
Again, in exploring the eastern shore of the great Wettern Lake, to the south of 
a stena, among the phenomena of great interest to which we shall elsewhere 
a vejt , we found that along the steep shores of the Omberg, one of the few hills 
m ° Ut 16rn Sweden where the granitic gneiss occupies a tract of any considerable 
rocks that H *1° rn ° U ' uistructive or truly original description of the structure and form of granitoid 
the Berlin A l " ^ ^ em ^ lacec ^ * n Baron Leopold von Bach’s recent memoir in the Transactions of 
that the st '• ' ,C ’ c ’ eDCes ' 1842. We have also great pleasure in saying, that we think it is probable 
friction b t ° !> £ ranb ‘ c rocks may in some instances be referred (as M. von Buch suggests) to the 
C mcnem ent of overlying masses over underlying domes of granite as resulting from struc- 
tural conditions. (See pp. 540 el scq.) 
geoloo-' -i r k°' en caPed our attention to a passage in the Swedish works of Hisinger, wherein that 
*o low \ ° C1 " t ' leSC m histone quarries, though in his time they were probably not worked down to 
Billi n „ T °' e aS at prcSent " " e ma }' further state, that this author’s maps and sections of the strata of 
that the n> ^ ** ° f Kmnekulle hdl Lower Silurian), are very faithful. On visiting Lugnos, we found 
Lard ark ' T " llsl0 " OS were s P b t off by horizontal fractures from vertical cylindrical columns, cat out of the 
surface mo' ^ * 18 WOrthy of remark, that in its separation, this regenerated rock flakes off with a 
been derived ^ imitatin ^ the sub j acent crystalline mass, from which it has 
detached * l V? ^ ° Pposite woodcut , in which the granitic rock is seen to exfoliate in situ, leaving 
M. von Bueh' a r ° 1< al f ™ Sments of its surface - and thu s forming the commencement of the felsen-meer of 
D 
