regarding the Rocks of the Red Sandstone For mation. 75 
tertiary basaltic streams to be seen, where olivine does not exist, 
while, at the same time, it abounds elsewhere ? Such instances 
occur in the Mittelgebirge, about Eisenach, in the Rhongebirge, 
&c. Olivine is certainly characteristic of the recent basalts, but 
it is nevertheless found also occasionally in ancient basalts, in 
contradiction to M. Beudanfs assumption, and it exists there 
especially decomposed, or as limbilite. Every body knows that 
this substance is rather easily decomposed and why, then, 
should it be deemed a matter of surprise not to find it in its 
original state in so ancient igneous deposites ? But happily we 
do not want the presence of this mineral to show the igneous 
origin of ancient basalts, — we do not even require to take notice 
of their augite : the porosities, the appearances and geognostical 
position of old basaltic rocks, are our unanswerable proofs of 
their igneous origin. Is it not clear, then, that these Neptunian 
proofs vanish of themselves, and that we have only to prove the 
truth of our assertion ? 
With regard to the amygdaloids, it would seem that the 
author of the Voyage en Hongrie had not paid sufficient atten- 
tion to the nature of these rocks, when he positively denies that 
they constitute the upper or under parts of igneous masses. 
(P. 198.) I admit, with great pleasure, that he may be right 
in as far as concerns the amygdaloidal masses observed by him- 
self; but I assure him that he would err egregiously did he wish 
to generalize this particular observation, for I could without 
hesitation point out a dozen of places where this phenomenon is 
perfectly well seen ; for instance, on the Fife coast in the coal- 
field, on the Kincardineshire coast in red sandstone, at Planitz 
in red sandstone, at Prague in transition-slates, &c. 
In contradicting M. Beudant, I do not by any means con- 
tend, that what I have just stated is always and invariably the 
case, any more than I would assert that lava-currents or basaltic 
dikes have always their upper or under parts evidently scorified; 
all this depends upon accidental circumstances: but I shall only 
observe to him, that the amygdaloid pretty generally takes the 
place of those scorified parts, or that they are very porous basal- 
tic rocks, infiltrated afterwards by various substances, which is 
entirely conformable with the observations of true basaltic lava 
streams. I comprehend perfectly liow, in examining solitary 
