224 DR JAMES GEIKIE ON 
contains irregular layers of amygdaloidal cavities, ranged along the central or 
middle zone of the bed. It is composed of plagioclase, augite, magnetite, and 
olivine, the last being often more or less altered into serpentine. Such is the 
average character of the rocks which immediately overlie the coal-bearing 
strata, and anamesites of similar appearance predominate in the island. They 
generally decompose with a rusty brown crust, and are frequently much broken 
up, weathering into irregular spheroids. On slightly weathered faces, the rock 
has often a dull greenish colour and somewhat earthy appearance. The most 
distinctly amygdaloidal portions of a rock, are usually of a paler shade, and 
more close-grained texture than the darker less porous areas by which they 
are surrounded, and, viewed from a little distance, the various parts of one and 
the same flow resemble a series of separate beds. This peculiarity, which 
is sufficiently striking, was noted by ForcHHAMMER, who remarks that ‘the 
amyegdaloidal rock alternates with the basalt, but these alternations shade into 
each other, and are not at all well-defined, but are very distinctly seen when 
the rock is looked at from a distance of some hundred feet. Then the different 
layers are seen with their different colours, and one finds that the junction line 
is parallel to the plane which the principal mass of the dolerite forms with the 
claystone (7.¢., tuff), and therefore parallel to the stratification.” 
The dark anamesite frequently becomes more coarsely crystalline, so as to 
assume the character of a typical dolerite, which is often rendered more or 
less porphyritic with plagioclase. This porphyritic character, however, is 
certainly much less common and less distinctly marked in the basalt-rocks of 
Suderée than in those of the northern islands. ForcHHAMMER, indeed, maintains 
that the traps above the coals are markedly porphyritic with “ glassy felspar,” 
while those underlying the coals are not porphyritic. Accordingly, he has in 
his map coloured all the northern islands and certain parts of Suderde and 
Myggenes as “dolerite-porphyry’—the remaining portions of Myggenees 
and the southern island, which are below the horizon of the coal, being 
distinguished as “dolerite without glassy felspar.’ We could not, however, 
trace any difference in Suderde between the basalt-rocks below and those 
immediately above the coals. At the same time, well-marked porphyritic 
and coarsely crystalline dolerites do occur in Suderde at some distance 
above the coal. In the mountain called Nakin, for example, there is a 
highly crystalline and porphyritic dolerite quite like many which occur in 
Stromée and Osterée. No hard and fast line, however, like that suggested by 
FORCHHAMMER, can be drawn between the beds above and those below the coal. 
The most that can be said is simply this, that while highly porphyritic 
dolerites prevail above the horizon of the coal, and therefore throughout the 
northern and smaller part of Suderée, and over all the northern islands, dark 
non-porphyritic and fine-grained rocks are the most common varieties met 
