384 SIGURDUR THORARINSSON 



augite, but most of the grains are basalt glass. The coating of these glass 

 grains consists of a diffusely double-refracting palagonite which gives the 

 sediments their characteristic yellowish-brown color. The cementing matrix 

 is basalt glass without palagonitization. 



The more coarse-grained sediment is more palagonitized. It contains the 

 same minerals: felspar, olivin and augite, as well as magnetite. Even here 

 basalt glass is dominant and the cementing matrix is glass. 



The great thickness of the Svinafell layers is rather striking considering that 

 to a large extent they are lacustrine. The thickness of the lacustrine facies 

 probably exceeds 120 m. The deepest lakes now existing in Iceland are found 

 either in tectonic depressions (Oskjuvatn, Thingvallavatn), in valleys over- 

 deepened by glacier erosion (Logurinn), or in glacier-eroded valleys dammed 

 up by constructive volcanic activity (Hvalvatn). As to the genesis of the basin 

 in which the Svinafell layers were deposited, the diastrophism seems not to 

 have taken any important part in it, whereas glacier erosion and damming 

 up by volcanic activity may have been the main factors. The later exposing 

 of the layers indicates both a great vertical erosion by ice and water and a 

 lateral erosion extending the strandfiat area during the latter part of the 

 Pleistocene. 



THE PLANT REMNANTS 



Macrofossils. As mentioned above, the interest in the Svinafell layers was 

 aroused when plant remnants were found there. 



A closer examination revealed that leaf impressions were rather abundant, 

 although far from evenly distributed in the sediments. They are plentiful in 

 Snidagil, fairly close to the old shore of the lake, and are especially frequent 

 in the gray layers B and E (cf. Fig. 4), but they are found in all layers of this 

 section that are accessible for closer study, i.e. all those beneath layer H. At 

 Breidagil they have been found in the entire pack of sediments, and the sandy 

 sediments of Godagil are rather rich in leaf impressions, especially of AInus. 

 Farther north, in Halsatorfugil, one leaf of a Salix sp. was found near the 

 tillite contact. 



The following plants have been found: 



Alnus. Leaf impressions of alder are by far the most abundant of all found 

 in the Svinafell layers. They are especially frequent in the gray layers B and in 

 E in Snidagil, probably because of proximity to the old lake shore. The species 

 has been determined by Svend Th. Andersen as AInus viridis (cf. PI. V). 



Betula. Only a few impressions of birch leaves have been found and only in 

 fragments. The species has not been determined. 



Salix. Leaf impressions of different species of willows have been found. One 

 leaf, found by Helgi Bjornsson in a scree in Snidagil, has been determined by 

 Svend Th. Andersen as Salix reticulata (PI. VII): one leaf, found by Th. 

 Einarsson, in layer F in Snidagil, is almost certainly Salix lanata (PI. VII). 



