308 Professor Jameson on Rocks Jvrnied by Hot Springs ^ 
ral perpendicular sections, is composed of .a rock described 
by Olafsen and Povelsen under the title, ‘‘ Saxum iopha- 
ceum alhidum columnar e sive basaltiformc^’' and which they 
say is named by the Icelanders Baula-stone, because it occurs 
only or principally in this mountain. It is either massive, 
or disposed in columns, having three, four, five,^ six, seven, 
eight or nine sides, and of a middling degree of hardness. Ex- 
ternally it is pale red ; internally it is whitish, and feels dry and 
sharp, and is lighter than true basalt. It does not effervesce 
with acids. They further remark, that it resembles other co- 
lumnai’ rocks in form, but differs from them in colour, feel and 
W'eight ; but agrees in so many characters with deposites found 
around hot-springs, that they consider the whole mountain as a 
thermal formation, which was at first soft, and in the state of 
bole, but was afterwards hardened by the influence of internal 
heat. These travellers found a rock of the same description on 
tlie summits of the highest mountains in Iceland, principally in 
the Westfiorden. A second thermal rock is described under 
the title, “ Saxum concretum tophaccum stratosum, cohre paU 
lidof and which is named by the Icelanders Hverhella. It 
is generally of a white colour, is more or less vesicular, some^ 
times inclines to vitreous, and possesses considerable hardness. 
It often occurs in large beds, which are either horizontal or ir^ 
regularly disposed, where hot-springs are in a state of activity, 
or in places where hot-springs formerly existed, but have long 
since ceased to play. Connected with both these rocks, there is 
a vitreous or glassy looking substance, of the nature of obsidian, 
but very different from the volcanic mineral of that name,-^the 
one being a product of hot-springs, while the other is perfectly 
melted volcanic glass. A third thermal rock is particularly no- 
ticed by Olafsen and Povelsen, under the name “ Saxum t(h 
pliaceum hrunneo^pallidum lithoooylis phytolithisque repletum.’^ 
It is of a brown colour, vesicular, but not to the same degree 
as tile preceding kind. It contains portions of vegetables more 
or less completely silicified. It is found in the vicinity of hoU 
springs, and in many districts where hot-springs were formerly 
in activity. A fourth thermal rock is named Saxum topha^. 
ceum simiUquatum nigricans tlicrmarumP This curious rock 
is of a black Qolour, and in hand specimens very much resem^ 
