140 
THE GEOLOGIST. 
these of irregular outline is crossed bj the Rhine at Andernach. Its 
western and more important part is about three miles long and two 
broad. The Laacher See is well known as a lake occupying an old 
crater in this part of the country, not far from Andernach. This dis- 
trict was described and illustrated by Dr. S. Hibbert, in 1853, in his 
' History of the Extinct Volcanos of the Basin of Neuwied,' etc. 
The other district, characterized by volcanic rocks and craters dis- 
persed over an area of about four miles by three, is at a short dis- 
tance to the south-west, and contains several large lake-craters, such 
as the Gemuuder Maar, the Pulver Maar, the Meerfelder Maar, etc. 
One of the old lava-streams in this area is met with at Bertrich, on 
the Ees, a small river running into the Moselle half-waj between 
Treves and Coblentz. Consisting of columnar basalt, and being per- 
forated by a natural aperture, this mass of volcanic rock presents the 
aspect of a basaltic colonnade, and has always attracted the attention 
of travellers, especially as the joints of the basalt, instead of taking 
a regular polygonal or angular shape, are more or less spheroidal, 
" so that a pillar is made up of a pile of balls, usually flattened ;"* 
hence the grotto at Bertrich is called the Kasegrotte, or Cheese-cave. 
" The basalt is part of a lava-stream, from thirty to forty feet thick, 
which has proceeded from one of several volcanic craters still extant 
on the neighbouring hills ;"t and, having run in the valley, it has 
since been partially destroyed and excavated by long-continued water- 
action. Mr. J. E. Lee has favoured us with a pencil sketch of this 
interesting Cheese-grotto, from which Plate YIII. has been engraved ; 
and, although the grotto is well known to geological students by the 
woodcut in Sir C. Lyell's ' Manual,' p. 386, yet we think that as 
the subglobular character of the basalt is very much better shown by 
our correspondent's sketch than in the little woodcut alluded to, we 
shall be doing good service by producing it here. 
In connection with the Cheese-grotto, Sir Charles alludes to the 
occurrence and characters of globular lavas and trap-rocks, adducing 
particularly the globiform pitchstone of Chiaja di Luna, described and 
figured by Mr. Poulett Scrope, in his account of the Ponza Isles (GeoL 
Trans., 2nd ser. vol. ii.). This pitchstone has the globiform structure 
near its junction with prismatic trachyte; and itself shows a ten- 
dency to the columnar division ; the columns, however, separating 
into large globes or ellipsoids, placed one upon another, and, when 
weathered, ]"eadily desquamating at a touch into numerous concentric 
coats, having a kind of onion-peel structure. Different degrees of 
the prismatic or columnar condition, passing into the concentric and 
nodular, are observable in many basaltic and trachytic lavas, as well 
as in older trap-rocks (diorites, etc.) ; and indeed granite not unfre- 
queutly shows a tendency to split and exfoliate in a similar manner. 
The explanation of the columnar and nuclear structure is well 
given on Mr. P. Scrope's ' Considerations on Volcanos,' etc., 1825 
(an admirable work, now out of print, but about to be revived, we 
hope). In chapter 6, p. 134, etc., the divisionary structure assumed 
* LveU's Mauual Gcol. p. 38?. t Ibid. 
