Intelligence and Miscellaneous Articles. 229 
their structure but also in their mineralogical constitution. Among 
them occur examples of the rocks which have received the names of 
dunite, picrite, and lherzolite, with some curious types composed of 
felspar and olivine. 
Among the older peridotites of Scotland a new and very interest- 
ing type is described from near Loch Scye in Caithness. It appears 
to have been originally a mica-picrite, but the whole of the original 
minerals have been converted into paramorphs, firstly by schilleri- 
zation and subsequently by amphibolization and serpentinization. 
In conclusion, it was pointed out that the discrimination between 
the effects of the changes described as schillerization and those 
known as uralitization, amphibolization, serpentinization, and 
kaolinization is of the utmost importance, not only to the petro- 
grapher but to the mineralogist. 
2. “ Boulders wedged in the Falls of the Cynfael, Ffestiniog.” 
By T. Mellard Reade, Esq., F.G.S. 
This paper briefly described certain phenomena of stream-denu- 
dation observed in the bed of the Cynfael, which has cut a deep 
channel through the Lingula Flags, the course of the channel being 
mainly dependent on the jointing of the rock. In one spot the 
upper beds at the top of the gorge have slid upon the lower along 
their dip, about 10° to north by east, so as to project over the 
stream like a corbel; and advantage has been taken of this to 
form a bridge by means of a slab of rock laid from the projecting 
mass to the top of the opposite bank. At another point several 
very large boulders are stuck fast in the channel, and the stream 
flows beneath them. The boulders could not possibly have been 
carried down the existing gorge, and they had not, the author 
believed, fallen from above. He suggested that they might have 
been carried down by the aid of ice, probably in the glacial period, 
when the stream ran in a wider channel, and that they had been 
polished by the action of the water. 
mo, XXVIII. Intelligence and Miscellaneous Articles. 
de ‘COMBINATIONS OF SILVER CHLORIDE, BROMIDE, AND IODIDE 
oY ITH COLOURING-MATTERS. BY M. CARY LEA, PHILADELPHIA. 
oa HILE studying these silver-salts in May last, I found that they 
had the remarkable property of entering into chemical combi- 
nation with many colouring-matters very much in the same way that 
alumina does, though not to the same extent, forming what may 
be called lakes. It is only necessary to bring freshly precipitated 
and still moist silver-salt into contact with the colouring-matter, 
or to make the precipitation in the presence of the colouring-matter 
if the latter is not precipitated by silver nitrate, when the combi- 
nation takes place and the colouring-matter cannot be washed out 
by any amount of washing. A prolonged absence following imme- 
diately after has prevented the continuation of the investigation. 
