PROJECTED EXPLORATION OF ICELAND. 
227 
But the observation of mocjeni glacial conditions in Iceland is not 
the only way in which existing phenomena can be used with advan- 
tage in the interpretation of by-gone history. The formation of the 
gypseous and saliferous marls of the Triassic series is very imper- 
fectly understood, and nowhere so well as in Iceland can be seen the 
operations of mud-springs charged with muriates and sulphates, such 
as form the well-marked features of the "red marl" deposits of 
England, and which may have resulted from some such operations of 
subterranean heat. 
The war between Huttonians and Wemerians is not quite so fierce 
now as when Sir George Mackenzie, himself a stout supporter of the 
great Scotchman, visited the volcanic tuffs and scorise of Hecla ; but 
many igneous minerals are yet unsolved, and very good help may be 
given by a careful study of the " Pearlstones," silico-aluminous 
deposits, and others so abundant in the volcanic regions of Iceland. 
Again, another field of observation was opened seventeen years 
ago by Prof. Ehrenberg, and has not, to our knowledge, been entered 
by any one since. Volcanic products erupted from the craters of 
Iceland have been carried in the shape of " meteoric dust" to a dis- 
tance of five hundred miles. A good example of this is the case of 
the ship " Helena" of Copenhagen, covered ^^-ith a layer of ashes and 
dust when at a distance of five hundred and thirty-three Enghsh 
miles south-east of Hecla. To this mountain, then in eruption, the 
cloud of wind-blo^Ti volcanic matter was traced, and the result 
showed that the same silicious-shelled infusoria contained in it were 
also to be met with in the dust which had settled upon the flanks of 
Hecla, and by colour, appearance, and contents, the transported dust 
was identical with that which had settled upon near-lying places. 
In connection with this, Prof. Ehrenberg suggests that it would be 
of the utmost value to secure samples of dry ashes of any kind that 
have not been wetted since their eruption ; and that if any traveller 
in the volcanic region was fortunate enough to be upon the mountain 
while ash or dust of any kind was being emitted, it would be im- 
portant to secure a specimen of such deposit before it had been sub- 
jected to atmospheric or aqueous influences, so that the important 
question may be settled whether organic bodies do exist in matter 
emitted from volcanic vents. 
