THE 
GHOLOGICAL MAG 
NEW SERIES. DECADE VI. were 
Pa SaARe een 2 cs 
No, IX—SEPTEMBER, 1916 SEP | 9 1916 
ORIGINAL ARTIC ee 
I.—Tse Buitpine vp or tHe Norra Ariantric TERT C 
PLATEAU. 
By LEONARD HAWKES, M.Sc. 
(PLATE XVI.) 
T is many years ago since Sir Archibald Geikie pointed out that 
the Tertiary basalts of the Western Isles of Scotland and North- 
East Ireland were remnants of plateaux built up of lavas extruded 
from fissures after the manner described by von Richthofen. In 
historic times fissure eruptions have taken place in Iceland, and 
in Zhe Ancient Volcanoes of Great Britain a chapter is included on 
‘The Modern Volcanoes of Iceland as illustrative of the Tertiary 
Volcanic History of North-Western Europe” (1, p. 260). Whilst 
little remains to be added in support of the very definite analogy 
exhibited in the nature of the lava streams themselves, the equivalent 
of the thin bands of red rock so typicaliy intercalated in the 'lertiary 
series has not been particularly examined, and I have visited Iceland 
in order to study the red beds themselves and search for their counter- 
parts in the modern lava deserts. 
THe Tertiary Series oF Icenanp. 
_ The Tertiary rocks of Iceland are similar in kind to those composing 
the volcanic series of the same age in the British Isles, only the 
development is on a much grander scale. The observable thickness 
is 11,000 feet, and how much has to be added on to this, top and 
bottom, it is impossible to state. The formation consists chiefly 
of basic rocks. In the east of Iceland acid types are largely 
developed, attaining im some places a thickness of 2,000 feet. 
Wherever I have studied them these acid rocks are dominantly 
extrusive in character. Occasionally remains of plants and trees 
together with considerable thicknesses of tuff and weathered material 
occur between the basalts, but these deposits are not particularly 
under discussion here. Analogous rocks compose the zone separating 
the upper and lower lavas in North-Kast Iceland, and their 
significance has been fully treated of in a recent memoir (2). Owing 
to their economic importance and plant-remains these beds have 
attracted most attention, but they occur only rarely in the series, the 
normal development of which is a succession of basalts separated by 
thin bands of bright-red rock. 
A detailed examination of a thousand-foot section at Begisa, 
Hyjatjord, North Iceland, showed thirty-eight basalts and partings 
DECADE VI.—VOL. III.—NO. IX. 25 
an lnStiz 
UY 2% 
oN 
“tional wuse®S 
; 
