THORODDSEN 



as already mentioned, in East Iceland calcareous spar is quarried 

 at Helgusta5ir near Reydarfjorftur and is used by the makers of 

 optical instruments. 1 



1 For fuller notes on the Physical Geography and Geology of Iceland the 

 reader is referred to the following papers by Th. Thoroddsen : Island. Grundriss 

 der Geographie und Geologic: Justus Perthes, Gotha. 1906 (358 pages). Lysing Is- 

 lands, Kobenhavn, 19081911, in 2 vols (365 and 673 pages). Explorations in Ice- 

 land during the years 1881 98 (The Geographical Journal. London, 1899. Vol. XIII, 

 pp. 251274, 480513). Vulcane im nordostlichen Island (Mitteilungen d. k. k. Geogr. 

 Gesellschaft, Wien, 1891, pp. 117145, 245289). Geological Map of Iceland. Sur- 

 veyed in the years 188198. Edited by the Carlsberg Fund. Copenhagen, 1901, 

 Scale 1 : 600,000. 



