By Nevil Story Maskelyne, U..A., P.R.S. 157 
of which have been re-distributed by aqueous action. Occasionally 
the quartz is crystallised and not apparently rounded, and, also 
occasionally, the chlorite mineral is seen to present itself in vermicu- 
lar forms of the kind to which the term “ helminth” has been applied. 
The minute crystalline structures termed microlites may in some cases 
(especially in the stone No. 9) be detected, and a few hexagonal 
prismatic nodules that are revealed in one or two microscopic sections, 
may possibly be apatite. A dark opaque mineral which is present 
to a small amount is probably pyrrhotine (magnetic pyrites), this 
mineral being present as an important ingredient in the stone num- 
bered 17. 
- The so-termed fluxional character presented in the distribution of 
the minerals in these stones, which is best seen in a section from 
the stones numbered 11 and 17, and is also a conspicuous feature of 
some of the stone chips and fragments Mr. Cunnington has collected 
from the ground immediately surrounding Stonehenge, is a charac- 
teristic structure to be borne in .mind in the search for their 
source. It is a by no means uncommon feature of this class of 
sedimentary rocks, built up of the disintegrated materials of older 
igneous rocks. The ground mass is seen in bent and wavy lines 
streaming round the little fragments of uncrushed rock or of felspar- 
erystals that are scattered through the mass, the contortions being 
often of sharp curvature and_ affecting all the neighbouring ground 
mass. 
Rocks from the silurian and Cambrian regions of North Wales 
and Cumberland can easily be found which present this structure, 
some of which, in the nature also of their material, resemble the 
rocks under description. Such, for instance, is a rock from Pen- 
maen, in Merionethshire, and certain of those from Cumberland and 
North Wales, recently described as “ volcanic ash” by Mr. Clifton 
Ward, resemble it in some points of structure. It is not however: 
a volcanic ash nor indeed do the microscopic features of many of the 
rocks so described appear to me to bear out this appellation. Some 
of them are undoubtedly much altered porphyries, and of others it is 
difficult to say at least from their characters as revealed by the. 
microscrope in what they differ from a sedimentary rock resulting 
