§2 REPORT—1857. 
In terminating these cursory notices, it may perhaps be not amiss to subjoin a few 
general considerations. . 
It would appear that the mineralogical characters of rocks are infinitely more varied 
and inconstant in Tuscany than anywhere else. The chief cause of the modifications 
locally presented by sedimentary rocks, is the abundance of the voleanic masses, them- 
selves also extremely diversified in their nature. The eruptions of these have taken 
place in a chronological order, very marked and distinct, exhibited by the modifica- 
tions they have induced in the various sedimentary rocks. 
Except the oldest granite, the protrusion of which is probably referable to the 
palzozoic epoch, all the other eruptions belong decidedly to the Tertiary period. 
The ophiolite or diallagic serpentine is the most ancient of them; to this succeed 
in chronological order, the euphotide or granitone; the diorite and ophite ; granite 
with tourmaline; the masses of siderolite and amphibolite; the quartziferous por- 
phyries; the recent serpentine without diallage; the trachytes; and finally, the 
basalts. ; 
The local disturbances partially produced by these eruptions do not correspond 
either to the systematic divisions elsewhere established or to the palzontological 
differences. 
The study of palzontology reveals a slow and graduated transition from the most 
ancient secondary strata up to those which are at present in course of formation, the 
fauna of each successive period assuming its own marked and constant character, 
while all are at the same time connected together by insensible transitions. 
Finally, in Tuscany also it is evident, and perhaps in ‘Tuscany it was first perceived, 
that the study of stratification is the only true key to open the secret and hitherto in- 
accessible paths of geological chronology. 
The Quartz Rocks, Crystalline Limestones, and Micaceous Schists of the 
North-western Highlands of Scotland, proved to be of Lower Silurian Age, 
through the recent Fossil discoveries of Mr. C. Peach. By Sir RopERicK 
I. Murcuison, D.C.L., FURS. 
At the last Meeting of the British Association at Glasgow, I communicated my 
opinion, founded on a survey with Professor Sedgwick in 1827, and confirmed by an 
exploration with Professor Nicol in 1855, that the quartz rocks, limestones, and mica- 
schists of Sutherlandshire, in which Mr. Peach had then detected a few imperfect 
fossils, would prove to be of Lower Silurian age. This belief was mainly founded 
on the physical succession of the various rock-masses, which I described as follows 
in the ascending order :— 
1. An ancient gneiss in part highly granitoid or traversed by granite veins. 
2. Coarse grit and conglomerate of reddish colours (formerly mistaken for Old Red 
Sandstone). 
3. Quartz rocks with intercalated limestones. 
4. Micaceous schists, &c., in parts almost gneissose, with quartz rock, &c. 
5. The great triple series of the Old Red Sandstone consisting of conglomerates and 
sandstone at the base, the Caithness ichthyolite flags in the centre, and the sandstones 
of Dunnet Head and the Orkneys above. 
My present view (as completed by the subsequent observations of Colonel James, 
R.E. and of Professor Nicol in the summer of 1856, is, that the coarse red grit and 
conglomerate No. 2 represents the Cambrian of the British Government Surveyors ; 
the quartz rocks, limestones, and micaceous schists, Nos. 3 and 4, having now proved 
to be what I suggested, viz. Lower Silurian rocks. 
My earlier sections and observations having led me to conclude that the base of the 
Old Red Sandstone or Devonian rocks reposed transgressively and discordantly upon 
those quartzites and mica-schists, I naturally inferred that if the Durness limestones 
and quartz rock were Lower Silurian in a metamorphic state, the Upper Silurian was 
omitted; thus accounting for the great solution of continuity which occurs. 
A recent discovery of Mr. C. Peach in the limestones of Durness has set the matter 
atrest: and asit has been a guestio vexata,—Mr. Hugh Miller having thrown out the 
hypothesis that these rocks might be metamorphosed equivalents of the Old Red and 
+ 2 aati 
