PHYSICAL GEOGRAPHY 



213 



ness (20 50 metres) in the north-western peninsula and was origi- 

 nally deposited at one level, but was afterwards broken up by dis- 

 locations, so that it now occurs at different levels above the sea. 

 The surtarbrand formation consists of diversely coloured layers of 

 clay and tuff with intercalated layers of lignite and coal-slate; in 

 many places leaves and fruits are excellently preserved in it, espe- 

 cially near Brjanslsekur on the northern side of Brei5ifj6ri)ur, and 

 at Trollatunga and other localities near Steingrimsi]6r5ur; in this 



Fig. 4. Mountains near KolviSarholl (tuff and breccia). 



last place it can be seen that large Tertiary woods have been des- 

 troyed by pumice-eruptions and lava-streams. According to O. Heer 

 the mean temperature of the year in north-w r est Iceland, at the time 

 of these Tertiary woods, was at least 9 C probably somewhat 

 more (11 12); now the average temperature for the year in these 

 places is only 2. The most common tree in western Iceland at 

 that time was Acer otopterix; its leaves are found in abundance 

 and excellently preserved in the clay-layers; there occurred in ad- 

 dition Sequoia Sternbergi, Pinus Steenstrnpiana , P. microsperma , P. 

 aemula, P. brachyptera, Betula prisca, Alnus Kefersteinii, Ulmus diptera, 

 Quercus Olafssonii, Liriodendron Procaccini, Vitis islandica, Rhus Brun- 

 neri, Dombeyopsis islandica, etc. 



The Palagonite formation is composed of different kinds of 

 tuffs and breccias, and in its upper divisions there is much moraine 

 material and scattered glacial gravel, as also some ice-striated lava- 



