?68 



NA TURE 



[Febkuary 20. 1902 



appalling floods, swept l)y Atlantic storms and sometimes 

 chilled by Greenland icebergs — these and other impressive 

 features have made Iceland a region of peculiar interest 

 to students of nature. To the geologist, in particular, the 

 country offers a wide field for observation. Its ice-fields 

 remain as relics of the Ice Age, and are still large enough 

 to illustrate inany of the characteristics of that period in 

 geological history. Its volcanoes display almost every type 

 of volcanic action, and present a marvellously extended 

 chronicle, stretching back from the present day through 

 the C'.lacial period mto older Tertiary time. The vicis- 

 situdes of its climate and the general absence of a pro- 

 tecting cover of vegetation afford singular opportunities 

 for the study of the progress and rate of denudation, 

 while its many hundreds of miles of coast-line furnish 

 inexhaustible materials for investigating the action of the 

 sea on the shores, and the causes which lead to the 

 advance or retreat of the land. 



That Iceland has been much less visited than such an 

 interesting region might have been e.xpected to be has 

 probably arisen mainly from two causes. In the first 

 place, it lies a good way off, across a stormy ocean 

 on which the means of communication are neither 

 so frec|uent nor so luxurious as modern requirements 

 demand, and, in the next place, when the traveller 

 reaches tlie island, he finds that to journey through it 

 involves, not only a good deal of expense, but exposes 

 him to privations which he is not always well able to 

 endure. Many who have shrunk from the voyage in face 

 nf these difficulties have longed for what comes next in 

 \ alue after an actual personal visit to a country— a good 

 map of it, on a sufficiently large scale and with enough 

 of detail to allow its main characters to be intelligently 

 grasped. Geologists will be glad to hear that this want 

 has now been supplied. They are well aware that for 

 some twenty years the indefatigable Icelandic geologist 

 Dr. Th. Thoroddsen has been at work, summer after 

 summer, mapping his native island and publishing from 

 time to time short notices of his investigations. Only a 

 few of these notices have appeared in English journals ; 

 more have been translated into German, but the fullest 

 and best accounts of his work are those in Danish, and 

 more especially the series of papers in the Gt-'ogin/isk 

 'lidskrifl published at Copenhagen from 1884 up to the 

 present time. Maps of various portions of Iceland, which 

 have accompanied some of these papers, have shown 

 with what skill and energy their author was carrying on 

 his self-imposed task, in the midst of all the known dif- 

 ficulties of Icelandic travel. The work on which he has 

 been engaged was rather the duty of a Government than 

 what can be expected to be undertaken by a private 

 individual. But he has stuck to it with courage until his 

 materials have grown ample enough to permit him to 

 embody them in a general map of the whole of the 

 island. 



This map is now issued in two sheets, printed in colours 

 and published at Copenhagen, with the help of the Carls- 

 berg Fund. It is on the scale of 1 600,000, or about 

 ten English miles to an inch, which is large enough to 

 show much detail that has never yet been expressed on a 

 single inap and summarised in so clear and intelligible a 

 manner. The title and explanations of signs and colours 

 are given in English. The map presents a more striking 

 picture of the geology and physical geography of the 

 island than has ever been before available, and contains a 

 vast fund of instructive information in regard to matters 

 not only of local, but of theoretic interest. 



One of the first features to catch the observer's eye, as 

 he glances at the distribution of the colours, is the wide 

 area occupied by the Tertiary basaltic plateau. This vast 

 underlying platform, on which all the later volcanic 

 manifestations have been displayed, still forms the surface 

 of most of the western, northern and eastern districts. Us 

 nearly horizontal sheets of dark brown rock ha\ e been 



NO. 1686, vol,. 65] 



cut into innumerable fjords and inlets on the coast, above 

 which they rise in long lines of mural precipice. Among 

 the basalts lie layers of terrestrial vegetation, the famous 

 lignites or " Surtarbrandur," the positions of which, where 

 known, are indicated on the map. The plateau is diver- 

 sified by the uprise of numerous masses of liparite and 

 granophyre, which are especially developed in the eastern 

 pari of the island. They may be compared with the 

 granophyre intrusions which have disrupted our own 

 Tertiary volcanic plateau in the west of Scotland. A 

 further coincidence between the volcanic geology of the 

 two regions is to be seen in the scattered patches of 

 gabbro shown on the map, though this rock does not 

 appear to play the important part in Iceland which it does 

 among our Western Isles. For the first time some 

 adequate conception can be formed from this map of the 

 extent and distribution of the palagonitic tuffs, breccias 

 and conglomerates, for which Iceland has so long been 

 noted. 



The post-Tertiary eruptions have broken out along a 

 broad belt of ground which crosses the island from south- 

 west to northeast. Dr. Thoroddsen separates the 

 "doleritic lavas" as a pre-Glacial and Glacial series from 

 the " post-Glacial basaltic lava" and the "post-Glacial 

 liparitic lava." Of the area and distribution of the huge 

 floods of basalt, which have transformed so many hundreds 

 of square miles of the interior of Iceland into black water- 

 less and verdureless deserts, we can now form a clear 

 idea. The vast expanse of the Od:idahraun, which has 

 been the scene of the most colossal outpouring of molten 

 material, can be seen in its true proportions. We can 

 realise, too, the source and extent of the great eruption 

 from Laki in the year 1783, which has been made so 

 familiar by the imperfect and incorrect notices of it 

 handed down in text-books. 



By a series of simple signs Dr. Thoroddsen has suc- 

 ceeded in separately indicating the positions of the great 

 lava-domes, comparable with those of Hawaii, such as the 

 massive Triilladyngja and others on the plateau of Odd- 

 dahraun ; of the volcanoes of \'esuvian type, built up- 

 of lavas and tuft's round a central orifice, like Hekia ; and 

 of the crater-rows, like that of Laki. The map shows 

 clearly the important place which this third type takes in 

 the vulcanism of the country. A further separation is 

 made of the "glacial volcanoes ' from those which are 

 "glacial and recent.' The positions of solfataras, hot 

 springs and mineral springs are marked, and space is 

 found for lines showing the trend of raised beaches and 

 the highest ascertained limit of submergence. 



Nor are the superficial formations omitted ; the various 

 Drift deposits of the uplands are represented by one tint 

 and those of the lowlands and valleys by another, while 

 on the south coast, the wide stretches of sand and mud, 

 discharged by the hundreds of streams that descend 

 from the great snow-fields and glaciers of the Vatnajokull 

 and the western Skaptafells district, are distinguished 

 from the other recent accumulations. An interesting 

 feature of the map will be found in the arrows that mark 

 the direction of the ice-stri;c on the rocks. These signs 

 indicate that while the general movement of the ice-sheet 

 has been outwards on all sides, each separate mass of 

 high ground has exercised an influence in guiding the ice- 

 drainage. This local effect is well brought out in the 

 north-western peninsula, where the slri;e descend into- 

 the fjords on either side of the main watershed. The 

 Glamu Jokull, which still caps that portion of the basaltic 

 plateau, is thus the lineal descendant of the ice-fields 

 that once spread over the whole island. 



In comparing the coast-line of diftercnt parts of the 

 island as depicted on this map, the geologist cannot fail 

 to be struck with the contrast between that of the 

 southern district and that of the rest. From Reykjavik 

 right round the western, northern and eastern sides of 

 Iceland, where the ancient Tertiary basalt-plateau meets. 



