44 
THK GEOLOGIST. 
occupies the North-eastern Highlands and a great portion of the eastern coast of 
Scotland ; fifthly, the Old Red series, arranged by the author into three divisions, 
the mi<l(lle being the Caithness flags. 
In the past autumn Sir Roderick, feeling that several points required stricter 
examination, revisited the country already describeii, extending his researches both 
east and west, and to the most northernly point of the Shetlands. 
In tills tour he not only confirmed his views previously ainiounced with regard 
to the succession of the older rocks, but examined the stnicture of the Orkneys 
and Shetlands, more clearly defining the relations and physical characters of the 
beds there composing the ()ld Red series. 
The jH-esent memoir comprised tiie details of these later observations ; and Sir 
Roderick acknowledged the aid he had derived from Mr. Peach (who accompanied 
him throughout the journey), Mr. Jnlni Miller, Rev. Mr. Gordon and others ; and 
he referred to the jn-evious memoirs of Mr. Cunningham and Hugh Miller on 
Sutherland, &c., and Dr. Hibbert on the Shetland Islands. 
The princii)le points dwelt ujion in this paper were — 
1. The evidence obtaine<l at various points, that the Lower Silurian hniestone 
is intercalated in quartz-rock (east of Loch Eriboll, Ass.ynt, &c.). 
2. That the Durness limestone lies in a basin supported by quartz-rock on the 
cast as well as on the west. 
3. That certain igneous rocks connected with the Durness trough are pro- 
traded near Smo, which had not i)efore been noticed. 
4. On this occasion corroborative evidence was adduced of the conformable 
superposition of the micaceous schists or gneissose flagstones to the quartzite 
series, the succession lieing visible at intervals in all the intermediate country 
between Loch Eriboll and Ledmore, and the passage upwards from the quartzites 
and their associated limestones into the schists and micaceous flags being both 
clear and persistent, with some local intemiptions only of igneous rocks. 
5. That the protrusion of porphyry, hypersthene, greenstone, &c. is not peculiar 
to any one line, but occurs in the purjile or Cambrian sandstone, in the overlying 
Silurian limestone of Durne.ss, ami again in the still higlier micaceous flagstones ; 
and that the latter, when intruded upon by granite, nnich resemble the old gneiss. 
6. With regard to the Old Red series of the east coast. Sir Roderick pointed 
out the extension of the middle set of deposits, namely, the Caithness flags, — 
their great thickness in Caithness compared with their develoiiment in the south, 
— and their range over the Orkneys into the Shetlands, where they also thin out, 
putting on a somewhat difterent lithological character, and where the Old Red 
series is chiefly represented by sandstones, the upper jiart containing plants. He 
dwelt upon the great value of the Caithness flags as ])aving-stones, their extraordi- 
nary durability being due to a certain admixttu'e of lime and liitumen (the latter 
derived from fossil fishes) with silica and alumina, whilst in some parts they con- 
tain bitumen enough to render them of economic value. The author next pointed 
out the passage of the Caithness flags upwards into light-colovu'ed sandstones, 
which eventually form the great headlands of Dunnet ami Hoy, where such over- 
lying sandstones cannot be of less thickness than 1,200 to 1,.500 feet. 
With regard to the micaceous rocks of the north-east of Scotland and the Shet- 
land Isles, they are, according to the author, portions of the series which is younger 
than the fossiliferous Lower Silurian rocks of the west of Sutherland, — the so- 
called gneiss of the Sutors of Cromarty belonging, in Sir Roderick's opinion, to the 
micaceous-flag series of eastern Ross-shire ; and the gneissic rock extending 
southwards to Flowerburu, Kinordy, and Rosemarkie, near Fortrose, is regarded 
by him as a member of that series, altered by the intrusion of granitic and fels- 
pathic rocks. 
The paper was illustrated by a large series of rocks and fossils collected during 
the author's last tour, and by geological ma]is, and coloured views and sections. 
December 1.5, 1858. — Prof J. Phillips, President, in tiie Chair. 
The following connnunications were read : — 
1. " On the Succession of Rocks in the Northern Highlands." By John Miller, 
Esq. Couunnuicated by Sir R. I. Murcbison, V.P.G.S. 
Mr. Miller in this communication explained the history of our knowledge of the 
