ERUPTIVE ROCKS AND METAMORPHOSED SILURIAN. 
13 * 
jectly identical in aspect with those of Shropshire and Herefordshire, rise out from 
eath the gieat mass of OIcl Red Sandstone of Ringerigge and Krokleven. In 
carrying the same section across to the gneiss range on the west bank of the river 
^rammen, the upper and calcareous coralline formation is separated from the black 
• ^d ur ian flags, by the same limestone with Pentamerus oblongus, which forms 
B 6 mterrnedia te bed between the Upper and Lower Silurian in many tracts of the 
utish Isles. These very clear general relations are illustrated in the accompany- 
ing woodcut. 
_ whilst we thus speak of the undoubted parallel, which, from practice in 
e e c ti n g the equivalents of rocks of this age, we have been able to establish 
en ^ le different members of the Silurian rocks of Norway and those of the 
ntis Isles, we must admit, that in many parts, particularly on the sides of the 
ays of Christiania and Drammen, they are so perforated " by eruptive rocks of 
posterior age, that, except in such very typical localities as those of Steens fiord 
and Krokleven, which appear to the left of the accompanying woodcut, it is diffi- 
cult to distinguish a clear order of superposition ; so much are the strata thrown 
in o un u ations. These intrusive rocks (t), whose characters and the effects they 
pio uce upon the strata they have invaded were long ago described by M. von 
uch, consist of granites, syenites, porphyries (including the hyperite of that 
author), greenstones, amygdaloids, &cd 
Perfectly distinct from the older granitic rocks associated with the gneiss, these 
tl ^ ma&S6S aie now d emonstr ated by our observations to be of younger age 
t e Old Red Sandstone, and they, therefore, play the same part in geological 
y as to ieat masses of the trappean rocks of English authors. Whether they 
6 di y ided into two groups of different age protruded at different periods to 
surface is more than our limited time enabled us positively to determine ; but 
may be lemarked, that, with the apparent exception of the large crystalled por- 
P yry of Ringerigge (p of woodcut and rhomb-porphyr of Von Buch), we nowhere 
saw any of those contemporaneous porphyries, greenstones, and other stratified 
'gneous masses which are so abundantly interlaminated with the Silurian rocks 
(pai ticularly the lower) throughout large districts in the British Isles, where in 
expanding such deposits they often necessarily obliterate the organic remains, and 
the ri_ ht r }i ead , er may form his idea of these infusions from the representation on a small scale towards 
a twentieth Jr® ° f the woodcut - though it is not pretended that the section (woodcut, p. 13) exhibits 
portion of the intrusions and flexures. 
c* 2 
