Oct. 8, 1885] 
NATURE 
559 
mica aud quartz, are developed. The most intense mechanical 
metamorphism occurs along the grand dislocation (thrust) planes, 
where the gneisses and pegmatites resting on those planes are 
crushed, dragged, and ground out into a finely-laminated schist 
(AGlonite, Gr. mylon, a mill) composed of shattered fragments 
of the original crystals of the rock set in a cement of secondary 
quartz, the lamination being defined by minute inosculating lines 
(fluxion lines) of kaolin or chloritic material and secondary 
crystals of mica. Whatever rock rests immediately upon the 
thrust-plane, whether Archzan, igneous, or Paleozoic, &c., is 
similarly treated, the resulting mylonite varying in colour and 
composition according to the material from which it is formed. 
The variegated schists which form the transitional zones between 
the Arnaboll gneiss and Sutherland mica-schists are all essen- 
tially mylonites in origin and structure, and appear to have been 
formed along many dislocation planes, some of which still show 
between them patches of recognisable Archean and Paleozoic 
rocks. These variegated schists (Phyllites or Mylonites) differ 
locally in composition according to the material from which they 
have been derived, and in petrological character according to 
the special physical accidents to which they have been subjected 
since their date of origin—forming frilled schists, veined schists, 
glazed schists, &c., &c. The more highly crystalline flaggy 
mica-schists, &c., which lie generally to the east of the zones of 
the variegated schists, appear to have been made out of similar 
materials to those of the variegated schists, but to have been 
formed under somewhat different conditions. They show the 
fluxion-structure of the mylonites ; but the differential motion 
of the component particles seems to have been less, while the 
chemical change was much greater. In some of these crystalline 
schists (the augen-schists) the larger crystals of the original rock 
from which the schist was formed, are still individually recog- 
nisable, while the new matrix containing them is a secondary 
crystalline matrix of quartz and mica arranged in the fluxion- 
planes. While the m/onites may be described as microscopic 
pressure-breccias with fluxion-structure, in which the inter-titial 
dusty, siliceous, and kaolinitic paste has only crystallised in 
part ; the azgen-schists are pressure-breccias, with fluxion-struc- 
ture, in which the whole of the interstitial paste has crystallised 
out. The mz/oni’es were formed along the thrust-planes, where 
the two superposed rock-systems moved over each other as 
solid masses ; the azgen-schists were probably formed in the 
more central parts of the moving system, where the all-surround- 
ing weight and pressure forced the rock to yield somewhat like 
a plastic body. Between these augen-schists there appears to 
be every gradation, on the one hand to the mylonites, and on 
the other to the typical mica-schists composed of quartz and 
mica, Like the mylonites, the crystalline augenites and mica- 
lites present us with local differences in chemical composition 
(calcareous, hornblendic, quartzose, &c.), suggestive of Archzean, 
igneous, or Palzeozoic origin. They also show similar structural 
varieties due to secondary physical changes (frilled, veined, 
glazed, &c.), as well as others due to the presence of special 
minerals (garnet, actinolite, &c., &c.). 
On certain Diatomaceous Deposits (Diatonite) from the Peat of 
Aberdeenshiie, by W. Ivison Macadam, F.C.S., F.S.C., &c., 
Lecturer on Chemistry, School of Medicine, Edinburgh.—The 
material was found below the peat in certain districts of Aber- 
deenshire, but principally in the basin in which lie Lochs 
Kinnord and Dawin. After removal of the surface peat-fuel, the 
lower and more highly mineral portion was cut in blocks and 
air-dried. The substance then consisted of almost pure Diatom- 
acea bound together by the rernains of Spragnum, Equisetacea, 
&c. Besides being found underlying peat the substance was also 
obtained on the shores of Loch Kinnord, and the more pure 
Diatoms were thickly distributed over the bottom of the deeper 
portions of the lake; these latter, however, from the want of 
the binding obtained from the marsh plants above mentioned could 
not be rendered readily available for market. An interesting 
point regarding these deposits was that whilst in Loch Kinnord 
an abundant supply of the Diatoms could be obtained, in the 
neighbouring Loch Dawin scarcely a single Diatom (recent or 
fossil) was found. This was probably due to the fact that whilst 
the feeding waters of Loch Kinnord flowed from hilis consisting 
of a coarse and much disintegrated granite, and consequently | 
contained a considerable portion of soluble silica, the Loch 
Dawin waters were obtained from hornblendic mountains, and 
held much less soluble silica in solution. The material was 
principally used for the manufacture of dynamite, and a con- 
siderable quantity had been forwarded to the works for this 
purpose. Unfortunately, however, dynamite had fallen to a 
great extent out of use, being replaced by the more powerful 
blasting gelatine, and thus what had at one time appeared as if it 
would prove an important local industry had entirely fallen away. 
Other uces, however, could be found for the material, such as 
the manufacture of ultramarine, for which, from the very small 
proportion of iron present, the diatomite has more especially to 
be recommended. As an absorbent it was of fully double the 
value ol the ordinary German varieties of ‘‘ kieselguhr.” 
On Some Ricent Earthquakes on the Downham Coast, and 
their Probable Causes, by Prof. G, A. Lebour, M.A., 
F.G.S.—For the last two years frequent slight shocks, 
resembling those of earthquakes, and accompanied by rum- 
bling noises, have been felt at Sunderland. Much discussion 
has arisen as to the cause of these, but that they are due to 
natural causes is now quite certain. Sunderland stands upon 
magnesium limestone, from 300 to 400 feet thick beneath the 
town; the rock is riddled with cavities of every size, some so 
small as to give a vesicular character to the stone, some large 
and forming true caverns. These cavities are partly due to the 
washing out of marly matter, partly to solution of the limestone, 
Every thousand gallons of Sunderland water contains one pound 
of stone ; in this manner about forty cubic yards of magnesian 
limestone are yearly pumped up by the Water Company, and of 
course a much larger quantity is removed by natural channels, 
This action enlarges the cavities ; the sides and roof fall in, thus 
accounting for the shock. The same explanation applies to the 
“breccia gashes” which are exposed along the shore. These 
are fissures filled with breccia. Quite recently similar shocks to 
those here referred to have been observed at Middlesborough. 
Pumping the brine from the salt deposits, 1c09 to 1200 feet 
below the surface, may produce cavities into which the rock 
falls. 
Some Examples of Pressure-Fluxion in Pennsylvania, by . 
Prof. H. Carvill Lewis. —The three localities in Pennsylvania 
described in this paper lie in an area which had been especially 
studied by the author for some years back and had led him to 
conclusions similar to some of those recently announced as the 
result of studies in North-Western Scotland, which have justly 
attracted widespread attention. (1) a zone of ancient crystalline 
rocks extends across South-Eastern Pennsylvania, near Phila- 
delphia, which is generally believed to underlie the lowest 
Cambrian strata and to be of Archzean age, This zone is about 
a mile wide where it crosses the Schuylkill River, south of 
Conshohocken, and it is from this point to Westchester, some 
twenty miles westward, that the present remarks especially 
apply. Although in many portions exhibiting a distinct gneissic 
lamination, the rocks of this zone are held by the author to be 
of purely eruptive origin, consisting of syenites, acid gabbros, 
trap granulites, and other igneous rocks, often highly meta- 
morphosed. It is the outer peripheral portion of this zone to 
which attention is here directed. While the rocks are massive 
in the centre, this outer portion has been enormously com- 
pressed, folded, and faulted, with the result of producing a 
tough-banded, porphyritic fuato gneiss identical with the 
‘milonite” of Lapworth or the ‘‘ sheared gneiss” of Peach 
and Horne. So perfect is the fluxion structure that the rock 
resembles a rhyolite. As in the ‘‘ banded granulite” of 
Lehmann, elongated feldspar ‘‘ eyes” lie in flowing streams of 
biolite grains and broken quartz, the streams often parting and 
again meeting around the porphyritic ‘‘eyes.” Occasional 
crystalline eyes of hornblende remain, but most of it has been 
converted into biotite. A point of especial interest is that the 
feldspar of the eyes is quite colourless and free from inclusions, 
like the sanidine of recent lavas, while, on the other hand, the 
feldspars of the inner and massive portions of the zone, out of 
which this outer portion has been reformed by pressure fluxion, 
are full of inclusions and have the ‘‘ dusty” appearance so 
common in ancient feldspars. The fresh-looking feldspar eyes 
are therefore believed to have been subsequently formed as a 
result of a recrystal/isation of the old material under the inflnence 
of pressure fluxion. In similar manner the biotite has been 
made out of the old hornblende, garnets have been developed, 
and the quartz has been granulated and optically distorted by 
pressure. The influence of pressure is also seen in certain 
Cambrian strata in the immediate vicinity, where a sandstone 
containing cylindrical casts of scolithus linearis, apparently 
identical with the ‘‘pipe-rock” of North-Western Scotland, 
has, like it, been compressed to such a degree that the vertical 
casts are flattened out and elongated in the dircction of lamination 
