162 
Mean wave- 
length of 
band or line 
Provisional 
name 
Position of lines 
in the spectrum Probability 
Absorption-bands ] { 443 Da New. 
in violet and? 451°5 Sa Dysprosium. 
blue. : \ | 475 SB New. 
Bright lines in— 
Violet. . . 456 Sy Ytterbium. 
Deep blue . 482 Ga New. 
Greenish - blue 
(mean of a 
close pair . 545 G8 Gadolinium. 
Green . 564 Gy New. 
Citron 574 G5 New. 
Yellow 597 Ge New. 
Orange 609 Sd New. 
Red .. 619 G¢ New. 
Deep red 647 Gn New. 
The initial letters D, S, and G recall the origin of the earths 
respectively from Didymium, Samarskite, and Gadolinite. 
Geological Society, May 26.—Prof. J. W. Judd, F.R.S., 
President, in the chair.—John Allen Brown was elected a Fellow 
of the Society. —The following communications were read :— 
Further proofs of the pre-Cambrian age of certain granitoid, 
felsitic, and other rocks in North-Western Pembrokeshire, by 
Henry Hicks, M.D., F.R.S., F.G.S. In this paper the author 
gave the results obtained by him during a recent visit to North- 
West Pembrokeshire. He stated that he had further examined 
some of the sections referred to in his previous papers, as well 
as others not therein mentioned, and that he had obtained many 
additional facts confirmatory of the views expressed by him in 
thove papers. The Lower Cambrian conglomerates and grits, 
he said, contained pebbles of nearly all the rocks in that area 
which he had claimed as of pre-Cambrian age ; and the frag- 
ments of the granitoid rocks, the felsitic rocks, the halleflintas, and 
of the various’rocks of the Pebidian series which he had found, 
showed unmistakably that those rocks had assumed, in all im- 
portant particulars, their peculiar conditions before the fragments 
were broken off. Moreover, he stated that there was abundant 
evidence to show that the very newest of the pre-Cambrian rocks 
of the area had been greatly crushed, cleaved, and porcellanised 
before any of the Cambrian sediments were deposited ; hence 
he maintained that there was in the area a most marked uncon- 
formity at the base of the Cambrian. At Chanter’s Seat, near 
St. David’s, he found that the Lower Cambrian grits and con- 
glomerates were, in parts, almost wholly made up of fragments 
of characteristic varieties of the granitoid rocks which form the 
Dimetian ridge near by. The so-called granite of Brawdy, 
Hayscastle, and Brimaston, he said, there was good evidence to 
show, was probably of the age of the granitoid rocks of St. 
David’s. The mass of so-called granite near Newgale, he 
stated, wis composed of rhyolities and breccias, undoubtedly of 
pre-Cambrian age. The Roch Castle and Trefgarn rocks, he 
stated, could not possibly be intrusive in Cambrian and Silurian 
strata, but belonged to a series of pre-Cambrian rocks. He 
referred to the important evidence bearing on the age of these 
rocks given in a paper communicated to the Society, since his 
last paper was read, by Messrs. Marr and Roberts. These 
authors showed that in a quarry near Trefgarn Bridge a Cam- 
brian conglomerate, overlain by Olenus-shales, is to be seen 
resting on the eroded edges of the Trefgarn series. The author 
examined this section lately, and obtained from the conglomer- 
ate some very large pebbles of the characteri-tic rocks called 
halleflintas, and of the ash-bands, both of which are found iz 
situ in the quarry. He therefore maintained that there was the 
most ample evidence to show that there was a great group 
of pre-Cambrian rocks exposed in North-West Pembrokeshire, 
and hence that he had proved conclusively that Dr. Geikie’s 
views in regard to these rocks, as given in his paper and more 
recently in his text-book, are entirely erroneous.—On sme 
rock-specimens collected by Dr. Hicks in North-Western Pem- 
brokeshire, by Prof. T. G. Bonney, D.Sc., LL.D., F.R.S., 
F.G.S. The author stated that he had examined microscopically 
a series of specimens collected by Dr. Hicks, and compared 
them with those described by Mr. T. Davies, in vol. xl. of the 
Quarterly Fournil, and with some in his own collection. He 
agreed with Mr. Davies’s conclusions in all important matters. 
The Chanter’s Seat conglomerate contained many grains of 
quartz aid felspar, curiously like those minerals in the so-called 
NATURE 
| mounting medium enabled objectives of small aperture to com- 
[Yune 17, 1886 
Dimetian, together with numerous small rolled fragments, about 
a quarter of an inch in diameter, exactly resembling the finer- 
grained varieties of that rock, besides bits of felsite, similar to 
some which occur in the St. David’s district, quartzite, a quartz- 
schist, and an argillite. The rocks iz si#w in the Trefgarn quarry 
were indurated trachytic ashes, together with the curious flinty 
rock which was the most typical of the so-called halleflintas, 
One of the pebbles from the overlying conglomerate perfectly 
corresponded with the last-named rock; others appeared to be 
most probably from an altered trachytic ash, differing only 
varietally from those iz sit, After prolonged examination 
of this ‘‘ha'leflinta” of Trefgarn and the similar rocks from 
Roch, he was of opinion that while it was possible that some 
specimens might be altered ashes, most of them were originally 
rhyolites or obs dians, devitrified, and then silicified by the pas- 
sage of water which had contained silica in solution. The 
Trefgarn group obviously could not be intrusive ia the Lower 
Cambrian, and it was extremely improba le that the Roch 
Castle series was newer than the basement conglomerate of that 
district. The Brawdy granitoid rock might be a granite, but at 
any rate it presented considerable resemblance to the ‘ Di- 
metian.” It was therefore evident that the Cambrian conglo- 
merate of St. David’s was formed from a very varied series of 
rocks, some of them much older than it, and that the Dimetian 
could not be intrusive in it. Moreover, even if the Dimetian 
should be proved ultimately to be a granite, and the core of a 
voleino which.had emitted the rhyolites, sufficient time must 
have elapsed after its consolidation and prior to the making of 
the conglomerate to remove, by denudation, a great mass of 
overlying rock. Hence, whatever its nature, it was pre- 
Cambrian.—On the glaciation of South Lan:ashire, Cheshire, 
and the Welsh border, by Aubrey Strahan, F.G.S., H.M. 
Geological Survey. By permission of the Director-General. 
The author stated that it may be concluded that (1) the striz on 
the English and Welsh sides respectively, while showing varia- 
tions among themselves, by a marked preponderance in one 
quarter of the compass, indicate a direction of principal glacia- 
tion, this direction being on the English side from about 
N.N.W., and on the Welsh fron about E.S.E. (2) The direc- 
tion of glaciation in both districts agrees very closely with that 
of the transportation of the drift, but is only locally influenced 
by the form of the ground. (3) The strice are by no means uni- 
versal, but are found almost exclusively in connection with those 
beds in the drift which contain evidence of the actual presence 
ofice. The stria are not such as can have been produced by 
valley-glaciers ; they go across and not down the valleys, nor 
are there any moraines. The marine origin of the drifts is indi- 
cated by their well-marked stratification as a whole, by the 
alternations of well-washed sands and gravels with the Boulder- 
clays, and by the occurrence through all the beds of marine 
shells. 
Royal Microscopical Society, May 12.—The Rev. Dr. 
Dallinger, F.R.S., President, in the chair.—The President re- — 
ferred to the death of Dr. J. Matthews, a member of Council, 
and a resolution of sympathy and condolence with the family 
was adopted.—Mr. J. Mayall, jun., exhibited and described a 
new pattern of the radial microscope by Mr. Swift, in which a 
rack was added to the arc, and a removable mechanical stage 
provided by which the object was clipped without any inter- 
mediate plate-—Mr. J. D. Hirst’s communication was read 
referring to the report in the Yowrnzal of the Royal Society of 
N.S. Wales, attributing to him the view that a highly refractive ~ 
pete in resolution with wide-angled oil-immersion objectives. 
Mr. Hirst explained that the report was so worded as to 
convey a totally erroneous impression of what he claimed, 
which was only that the highly refractive medium would render 
difficult test diatoms so easy to a good high angled water lens 
that the superiority of the oil-immersion objective will not be 
apparent, except under the very deepest eye-pieces.—Mr. C. D. 
Ahrens’s paper, on a new polarising prism, was read ; also Prof. 
Thompson’s letter in commendation of it as unrivalled for use 
as a polariser, having flat ends, wide angle, and absence of 
distortion or coloured fringes. —Dr. Sternberg’s paper on AZicro- 
coccus pasteuryi was read, in which he called attention to the 
characters which distinguish it in a very definite manner from the 
microbe of fowl-cholera, it differing from the latter, not only in 
its morphology, but in the fact that it is not fatal to fowls.—Mr. 
F. H. Evans exhibited sone photomicrographs produced by the 
Woodburytype process from negatives by himself, and transferred 
