T. Mellard Reade—On the Lower Trias. 549 
mechanical separation with a view to chemical analysis. Isolation 
with the Borotungstate solution was indeed tried by Mr. Player, but. 
without success. Lossen! states that the porphyritic crystals, in 
the keratophyres described by him, are, in great part, mechanical 
admixtures of orthoclase and albite, similar to microperthite; but in 
the rocks under consideration I have been able only in quite isolated 
instances to record the presence of micro-perthite structure. 
The rocks embraced in Group III. are slightly more crystalline 
than the others, the ground-mass being in general microcrystalline 
instead of cryptocrystalline. No. 12 (Little Arklow Rock) indeed 
has been placed by Haughton? among his soda-granites; but the 
structure of this rock can scarcely be termed granitic; at most it 
could only be called microgranitic (in Rosenbusch’s sense of the 
term), since it consists of porphyritic crystals imbedded in a micro- 
crystalline ground-mass. 
It only remains to point out that the modern equivalents of these 
ancient felsitic lavas are the rhyolites or liparites and pantellerites, 
which have been subdivided by Rosenbusch ’ into potash-liparites, 
soda-liparites and pantellerites, sanidine being the porphyritic con- 
stituent characteristic for the first, albite for the second, and anortho- 
clase for the pantellerites. The main difference between the liparites 
and the felsites lies in the character of the ground-mass, the glassy 
base of the former being replaced in the latter by the cryptocrystal- 
line aggregate known as felsitic matter.* 
Some of the rocks, especially those of Group I., show indications 
of having consolidated as true glasses (pitchstone or obsidian), as 
has been proved to be the case in several instances among the 
felsites of Shropshire and Wales by the valuable researches of S. 
Allport® and F. Rutley,® who have succeeded in detecting distinct 
traces of perlitic and spherulitic structure in these rocks. The 
Welsh felsites are of the same age (Bala) as the Irish rocks, and 
probably belong to the same series of volcanic outbursts. 
TV.—PuystocRaPpHy oF THE Lower Trias.’ 
By T. Meuiarp Reavpsz, C.E., F.C.S., F.R.E.B.A. 
Introduction. 
HE origin of the Triassic rocks of Britain is a question that has 
excited from time to time much interest and varied speculation. 
The entire absence of fossils in the Lower Trias or Bunter Sand- 
stone has led the majority of geological reasoners to look to causes 
1 Jahrbuch d. k. Preus. Geol. Landesanst. fiir das Jahr 1884 (1885), p. xxxil. 
2 Trans. Roy. Irish Acad. vol. xxi. pt. ii. (1859), p. 609. 
3 Mikros. Phys. vol. 1. 1887, p. 528. 
4 Nothing of the nature of microfelsite (in Rosenbusch’s sense) has been observed 
by me during the examination of these rocks. 
5 On the Pitchstones and Perlites of the Lower Silurian District of Shropshire, 
Q.J.G.S, vol. xxxiii. (1877), p. 449. 
§ On Perlitic and Spherulitic Structures in the Lavas of the Glyder Fawr, 
N. Wales, Q.J.G.S. 1879, p. 508 ; and in Memoir of Geol. Survey on the Felsitic 
Lavas of England and Wales. 
7 Read at the Brit. Assoc., Newcastle-on-Tyne, in Section C. (Geology), Sept. 
1889. 
