Dr. OC. Callaway—The Archean Controversy. 319 
- VI.—Tue Present State oF THE ARCHHAN CONTROVERSY IN 
Briain. 
By Cuaruzs Caniaway, D.Sc., F.G.S. 
Wea Archeean question in this country may be said to be about twelve 
years old. Rocks older than the Cambrian had indeed been 
recognized by Murchison and Sedgwick, and brief notices of Pre- 
Cambrian masses at St. Davids had been published by Salter, Hark- 
ness, and Hicks; but the Archean campaign was formally opened 
by Dr. Hicks in a paper read before the Geological Society in 
November, 1876. The attack upon the old views was followed up 
by Prof. Bonney, the Rev. Edwin Hill, Prof. Hughes, and myself, 
and, more recently, by Prof. Lapworth and Prof. Blake. The 
defence has been conducted by Dr. A. Geikie. The controversy has 
been animated, and not without sensational incidents. Great 
diversity of opinion has existed even amongst the assailants, and 
many important divisions of the inquiry must be still regarded as 
unsettled. The most noteworthy difficulty which has arisen in the 
progress of our work is the dynamic theory of metamorphism. 
My chief purpose in writing this paper is to show how far this 
theory affects our old conclusions; but I shall incorporate any facts 
necessary to give a true outline of the present state of opinion on 
the Archean rocks. J use the word “Archean” as_ strictly 
equivalent to ‘‘ Pre-Cambrian.” 
St. Davins.—Dr. Hicks originally described’ two groups, the 
Dimetian and the Pebidian. He subsequently” introduced an inter- 
mediate formation, the Arvonian. According to Dr. A. Geikie,* the 
Pebidian is merely the base of the Cambrian, while the Dimetian 
and Arvonian are granites and porphyries intrusive in the bedded 
rocks. Prof. Blake* regards all Hicks’s groups as Archean, but he 
would convert them into one continuous series. I cannot speak 
from adequate personal examination of the ground; but analogy 
with other districts would rather suggest to me that the granite and 
porphyry (the Dimetian and Arvonian) form a group distinct from 
and older than the Pebidian, and that the Pebidian also is Pre- 
cambrian. 
SHROPSHIRE.—Out of the “intrusive greenstones”” of Murchison 
and the Survey, it has been found possible to construct two well- 
marked Archean groups.? The older of these, consisting of granite 
and gneissic rocks, I have called Malvernian, from their probable 
equivalence to rocks of the same character at Malvern. But the 
new views of metamorphism deprive the term ‘equivalence ”’ of its 
ancient meaning. The rocks in question are granites and diorites, 
which under the influence of earth-pressures have here and there 
acquired a gneissic structure. These igneous rocks are alike in the 
two localities, the results of the metamorphism are similar, and 
there is in both cases a marked unconformity to the Cambrian. We, 
1 Quart. Journ. Geol. Soc. 1877, p. 229, 
2 [bid, 1879, p. 285. 3 Ibid, 1883, p. 261. 
* Quart. Journ. Geol. Soc. 1884, p. 294. 5 Ibid, 1879, p. 643. 
