Correspondence—Prof. W. King. 47 
(4) Grooved and striated surfaces are preserved under favourable 
circumstances. A full description is given of a number of instances, 
the direction of the strise being recorded, as well as the fall in feet per 
mile from the summit of the Beacons. The author in summing up his 
observations comes to the conclusion that the erratics in the Kgl wysilan 
and Caerau group were probably, as a rule, transported by floating ice, 
but that some may be the relics of old moraines; that the Boulder- 
clay of South Brecknockshire is chiefly the product of land-ice; and 
that the striated rock-surfaces are in some cases the result of glaciers 
which have descended existing valleys. In other cases they may have 
been produced by an ice-sheet, which it is possible may have come 
from the N.W. 
@@ ier set SS @ aN ei see NG ae 
Pee 
TEXT-BOOK OF GEOLOGY BY ARCHIBALD GEIKIE, LL.D. 
Str,—It is very far from my desire to write a word in derogation 
of the high merits which this work possesses ; but I may be allowed 
to draw the attention of its author to a few points personally affect- 
ing myself, and to some extent my colleague, Dr. Rowney. 
Dr. Geikie has incorrectly represented the view we hold as to the 
origin of the “canal system” of “ Hozoon Canadense.” Coupling our 
names with that of Professor Mébius, the readers of the Text-Book 
are informed that we “have endeavoured to show that the supposed 
canals and passages are merely infiltration veinings of serpentine 
in the calcite” (p. 639). This remark may be correctly applied to 
Dr. Mobius; but in none of our publications is there the least in- 
dication of any endeavour of the kind to be found. We have, on the 
contrary, maintained that the “canal system” has originated, in 
many cases, from the wasting action of carbonated solutions on 
clotules of “flocculite,” or, it may be, saponite—a disintegrated 
variety of serpentine, and, in others, from a similar action on crystal- 
loids of malacolite (‘‘ white pyroxene’). In both cases there are 
produced residual “figures of corrosion,” or arborescent configurations, 
having often a “regular disposition,” even to the extent of a sheaf- 
like symmetry.!. This, in which we certainly agree with Dr. W. 
B. Carpenter, is “quite unlike any mineral infiltration ;” for, as 
stated in our Old Chapter of the Geological Record, p. xviii, we had 
palpable evidence that it had been determined by mineral cleavage — 
a divisional structure, which is essentially regular and correspond- 
ingly symmetrical in malacolite and its monoclinic allies.’ 
While on the subject of Hozoonal structures, it behoves me to 
mention that the Text-Book contains no reference to our views, 
1 Formerly, I held with Dr. Rowney, that the “canal system’’ is in general 
irregularly arranged; but having been lately favoured by Dr. Carpenter with an 
inspection of his numerous beautiful preparations, besides having examined some 
specimens that have lately come into my possession, I feel bound, and in agreement 
with my colleague, to give expression to the terms stated in the text. 
2 The mineral origin of the “canal system’’ is demonstrable by the clearest 
evidences, hereafter to be published, abounding in specimens of hemithrere, inter- 
mixed with ordinary gneiss, which I have lately received from Ceylon. 
