64 Dr Daubeo y on the Columnar Structure of Trap Rocks. 
contain any part prior to the 3d book, and that it consequently 
cannot have been that which is now under consideration. 
( To be concluded in next Number.) 
Art. IX. — Remarks on the Columnar Structure of Trap- 
Rocks By C. Daubeny, M. D. M. G. S. Communi- 
cated by the Author. 
late M. Faujas St Fond, in his work on the Vivarais, 
has given us an interesting account of several of the Coulies of 
Lava, which, at very early periods, although subsequently to 
the last retiring of the waters, streamed down from the then 
existing volcanoes into the valleys situated at their bases. 
The perfect manner in which many of these torrents of lava 
may still be traced from the summit of the mountains, and even 
from the very craters whence they were ejected, did not excite 
in my mind a stronger interest than was caused by observing 
the close analogy which these igneous products often present to 
the basaltic rocks of countries, in which the existence of vol- 
canoes has never hitherto been made out. 
In following the track of these streams from their apparent 
sources, we are struck with the increasing solidity which they 
assume in the course of their descent, so that as we approach 
the valley which constitutes the limit of their progression^ they 
lose by degrees the porous texture that originally belonged to 
them, and put on the character of a compact, and often colum- 
nar form of basalt. 
The inferences, with respect to the igneous origin of the latter 
class of rocks, from the analogous appearances presented by 
these volcanic products, are of the same description, and subject 
to the same limitations with those I have attempted to deduce 
in a paper published in the Edinburgh Journal, from my ob- 
servations in Auvergne ; but on the columnar form which this 
lava so often exhibits, where it occupies the lowest part of the 
^ The substance of a paper read before the Geological Society, June 2. 1820. 
