THE TERTIARY BASALTIC FORMATION IN ICELAND. 93 



13. The Tertiary Basaltic Formation in Iceland. By J. Starkie 

 Gardner, Esq., E.L.S., F.G.S. (Read December 3, 1884.) 



A GRANT from the Government Fund enabled me to visit Iceland in 

 1881, with a view of studying its interbasaltic flora. I explored a 

 C3nsiderable par^ of the island and visited every locali-y that I could 

 reach where lignite had been met with. I did not take notes of 

 some of the localities where my visits were hurried ; but the con- 

 clusion I invariably arrived at was, that the sedimentary deposits 

 in which vegetable remains are found, are situated among the glassy 

 rhyolitic flows above the columnar series of basalt. The rhyolites 

 are usually pale in colour, and with banded structure, but are some- 

 times black pitchstone or obsidian. They cap the loftiest mountains 

 of the district west of Akreyri, and extend at least to Baula, a 

 mountain in the same latitude as Snaefell, and possibly beyond this. 

 They also occur on the east coast, though I did not reach any of 

 them in that part of Iceland, which I only visited from the Danish 

 mail-boat, which calls in many of the fiords. I did not pay par- 

 ticular attention to their thickness, but at Sandafell I measured 30 feet 

 of white, pink, ivory-coloured, and black glassy lavas. The thickness 

 is, I believe, sometimes greater than this, and they are interrupted 

 and overlain by smaller flows of basalt. The horizon is, however, 

 certainly continuous, and marks a very definite stage or phase in the 

 great series of Tertiary eruptions which extended from Ireland to 

 Iceland in Eocene times. 



I cannot yet present data to show how much younger this part of 

 the Icelandic series may be' than the columnar division of the forma- 

 tion in Ireland. Being near the southern limit of the flows, the series 

 may have ceased to be formed at a far earlier period in Ireland than 

 further north ; and this I believe to be the case, as there are no frag- 

 ments of glassy lavas in the Boulder-clays of Ireland. Denudation 

 may, however, have swept very much of the basalt away. There is no 

 base to the formation exposed in either Iceland or the Faroes, and we 

 are therefore ignorant of its total thickness ; but some of the moun- 

 tains reach an altitude of 6000 feet, and are still within its limits. 

 Iceland, like Ireland and Scotland, has also sufl'ered very great denuda- 

 tion. The mountains of the north and east coasts average some 

 2000 feet in height, and are entirely eroded out of horizontal sheets 

 of basalt. The valleys radiate towards the sea, and many form fiords 

 of considerable size. On the east coast especially, the only remains 

 of the highest layers of basalt are pinnacles or columns along the 

 mountain tops. The mountains are wall-like and continuous, with 

 few lateral openings of no great breadth, and flat-topped in most 

 regions. Their sides are precipitous, except where masked by 

 talus. Glaciation is very conspicuous, and every valley is occupied 

 by a rushing torrent fed by the melting snows of the interior, so 

 that travellers cannot proceed on foot for any distance, except to- 

 wards the interior. The rarity of dykes is one of the most noticeable 

 features of the basalts ; on one occasion I only observed one in a 

 ^Q.J.G.S. j^o.162. I 



