Dr. C. Callaway— The Archean Controversy. - 828 
It was obvious from these discoveries that the sequence in the 
Older Archzans would have to be differently interpreted. It ceased 
to be a succession in time, and was useful merely as a description of 
the distribution of the respective rock-types. But what we lost in 
one direction we gained in another and more important one. An 
empirical sequence was replaced by a revelation of true causation. 
Thus, the halleflinta, quartz-schist, and grey gneiss are produced 
from felsite by pressure, the limestone is formed from the same rock 
by segregation, the dark gneiss is modified diorite, and the granitoidite 
is a true granite intrusive in the felsite, the diorite, and their 
modifications. 
Prof. Blake in his paper+in the Journal of the Geological Society, 
and in his Report* to the British Association in 1888, agrees that 
the rocks in question are Archean, that the Newer Archeans are 
largely sedimentary, that the granitoidite is a true granite, and that 
the diorite has sometimes been modified into schist; but he does not 
admit that the grey gneiss and associated schists are of igneous 
origin, and he contends that the Lower and Upper Archeans form 
a continuous series. 
Tue Hieguianps or Scottanp.—The history of recent discovery in 
this remarkable region has been so well told by Prof. Bonney,’ Prof. 
Lapworth,‘ and the officers of the Geological Survey,’ that repetition 
is unnecessary. It is agreed on all hands that the Hebridean gneiss 
is Archean ; but there is not the same consensus of opinion as to the 
age and origin of the Hastern gneiss. In my chief paper® on the 
Highlands, I showed that, by enormous thrusts from the east, the 
Hebridean had been forced over the Ordovician (or Cambrian) rocks 
for great horizontal distances, and that the Hastern gneiss overlay 
the Ordovician in a similar manner. As the younger gneiss was a 
truly metamorphic rock, quite unlike any of the Ordovicians, I in- 
ferred its Archean age, and called it ‘“‘Caledonian.” In the debate 
on my paper, Prof. Lapworth, who had visited the Erribol district, 
said that the sections he had seen there seemed to support my view. 
Indeed, in the state of our knowledge at that time, no other inference 
appeared to be possible. However, Prof. Lapworth soon after re- 
visited his old ground, and in 1884 we were startled by the extra- 
ordinary theory that the Eastern gneiss was a melange of Hebridean, 
Ordovician, and igneous, rocks, which, under the influence of the 
great thrust, had been sheared out and in part recrystallized. In 
the following year, the Survey admitted the new conclusions, even 
to the length of adopting Prof. Lapworth’s view of the origin of the 
Eastern gneiss. I have not been to the Highlands since 1882; but, 
considering the nature of the evidence adduced, and the competence 
of the witnesses, as well as the confirmatory proofs I have collected 
in Ireland and at Malvern, I am disposed to concede to the new 
theory a high degree of probability. 
1 1888, p. 463. 2 p. 367. 
5 Presidential Address, Quart. Journ. Geol. Soc. May, 1885. 
* Guou. Mac. 1888, p. 97. 
Quart. Journ. Geol. Soc. Aug. 1888, p. 378. 
6 Quart. Journ. Geol. Soc. Aug. 18838, p. 356. 
