II. CONDITIONS PERTAINING TO SURFACE 



AND SOIL. 



AFTER having thus given a brief, general survey of the orographical 

 and geological conditions and having described the substratum 

 and general structure of the island, we will now pass on to a de- 

 scription of the surface itself, with which plant-growth is more parti- 

 cularly associated. As mentioned above, Iceland is built up of basalt, 

 tuffs and breccias, but basalt is the fundamental rock; the tuffs 

 and breccias are, for the most part, nothing else but basalt split 

 and pulverized. The mineralogical and chemical composition of the 

 soil is therefore essentially the same over the entire island, provided 

 the siliceous liparites are excepted which have no effect of any 

 importance to the whole. 



Seen from a distance, the basalt mountains usually appear to 

 be steeper than they are in reality, and the small terraces or 

 steps of the layers of basalt are not distinguishable in the higher 

 part of the mountain from a distance except when they are snow- 

 covered or when, as rarely happens, a scanty vegetation (especially 

 mosses) has been able to gain foothold upon the narrow ledges. 

 The rule is that the steps of the basalt mountains become broader 

 as the base is approached. At the top the separate layers project 

 as a narrow ledge which is only half, one, or two metres broad, 

 but lowest down in the valleys, and nearest to the sea the separate 

 layers form enormous terraces which may attain a breadth of */*- 



*} * 



l /2 km. or more. The upper surface of these broad terraces is covered 

 with gravel and clay, and sometimes with a scattered plant-growth, 

 or sometimes with a continuous vegetation, with bogs or swamps; 

 there, enormous, elongated snow-wreaths may persist far into the 

 summer. On basalt mountains erosion is more active on the sunny 

 side, therefore the other side is steeper and more sparsely covered 

 with plants. On the sunny side the average inclination is usually 



