25^ Sir George Mackenzie's Observations on Menge’^s Journey. 
do not know ; as it has no peculiar properties to distinguish it 
from the water of an ordinary river. 
I am totally at a loss with respect to his notion of the hot^springs^ 
producing lava, basalt, and trap-porphyry. Is it possible that 
masses of these, in a state of decomposition, could be mistaken for 
the act of their formation. ? Be this as it may, I liave always been 
an advocate for the agency of water strongly heated ; and I be- 
lieve I am the only Huttonian who has ever pretended, that the 
fundamental principle of onr theory, Heat acting under com- 
pression, rendered water a most powerful chemical agent. Most 
of the operations ascribed to your cold Neptunian element, I must 
always consider as imaginary ; but those of Plutonic water may 
have done much, and will yet do more^ — as the two elements com- 
bined may probably relieve us of much disputation, and at length, 
unite two theories, wliich are clearly both right and both wrong, 
since the one sometimes explains what the other does not. “ In 
Iceland,” says Menge, “ we find Volcanic and Neptunian forma- 
tions conjoined ; the connecting link between the two (transi- 
tion being the Volcanic-Neptunian formation, which appears 
to be produced by hot-springs.” I feel somewhat affronted that 
old Pluto has not been invited to join the party ; — you will find 
him below, you may depend upon it. I really did not expect 
to be believed in the account I gave of the rocks of Iceland, at 
the time I published it, and I have waited impatiently for the 
result of a visit by a Wernerian. I could not desire more than 
what Menge has said of the tract I examined, that, with little 
exc*eption, there is no true Neptunian trap in it. My views will 
not now beconsidered as having been taken with a prejudiced eye; 
I think that Menge has attributed more than enough to the 
hot-springs, Because I consider, that their external deposites 
are probably as different from the results which occur below 
ground, as stream-lava is from what it would have been had 
it cooled under a powerful compressing force. It is probable, 
that after he has seen the west of Iceland,, including Snasfell 
Syssel, he will form a different opinion of the relative posi- 
tions of the trap and volcanic districts. His Volcanic-Neptunian 
rocks j are my Submarine LavaSj and his ideas of the veins are 
somewhat Huttonian. I suspect that when Menge sees the hot- 
springs at Beikholt, he will find that they issue from rocks that 
are not truly volcanic. Yours sincerely, ♦ 
Fdinburgh, Jan. 1820. G. S. Mackenzie. 
