August 29, 1878] 



NATURE 



Ml 



iron formed by the agency of Penecilliiv, which accumulate in 

 large sponge-like masses so as to intercept the flow of the water. 

 The author points out the connection between such deposits and 

 iron-ore formations. 



Notes on some New Fossils " Eribollia 3Iackayi,'" from the 

 Quaj-tzites of Loch Eribol and other Parts of the Western High- 

 lands of Scotland, by James Nicol, F.R.S.E, (with photograph 

 of the rock), — The fossils were discovered by Mr. Donald 

 Mackay, early this year, in the Assynt quartzites of Lough 

 Eribol, lying below the Durness limestones, in which fossils 

 have been more abundantly found. The surface of the rock 

 shows the ends of more than a dozen bodies, more or less 

 rounded in form, running down into the interior of the stone, and 

 tapering to a point. They show a central core with an outer 

 wall around it. There is no doubt they are organic. The 

 author rather inclines to regard them as corals approximating at 

 least in form to Cyathophyllidce. Thin slices might perhaps 

 decide this question, but meanwhile the author has named 

 them Eribollia Mackayi, indicating the locality and the finder. 

 These and other fossils give the author no reason to reverse the 

 relations of the strata in the north-west Highlands held by him, 

 but much to confirm them. 



Concerning the Extent of Geological Time, by Rev. M. A. 

 Close, F.G.S. — Since geology has her own strong and unrefuted 

 arguments for the great extent of geological time, it is not 

 logically necessary for her to do more than show, if it can be 

 shown, that the physical arguments for the very inconvenient 

 restrictions thereof rest upon still unproved assumptions. The 

 argument from the rate of cooling of the earth seems to have 

 been satisfactorily shown by Mr. T. Mellard Reade to be quite 

 inconclusive. The argument from the probable duration of the 

 sun's radiation of heat assumes, inter alia, that the original 

 nebula from which the solar system was formed was cold, and 

 also that the unit of gravitation relatively to the mass of that 

 system has been constant from the time when that mass began 

 to fall together, and throughout the enormous interstellar dis- 

 tance which has doubtless been traversed by it since that time. 

 Dr. CroU's suggestion in answer to the former of these assump- 

 tions is logically sufficient as a reply to the whole of this argu- 

 ment. Nevertheless it may be added, as to the latter assumption, 

 that those physicists who have entered upon certain speculations 

 as to the cause of gi-avitation, cannot deny that it is per- 

 fectly credible, and even probable, that gravitation is not an 

 essential accompaniment of matter, and that the unit of grari- 

 tation may not be constant throughout all time and space. 

 The arguments from the earth's figure in connection with the 

 retardation of her rotation by the ocean tide depends on 

 the doctrine of the steel -rigidity of the earth taken all together, 

 as do also the calculations of various writers on subjects M'hich 

 bear in different ways on the present one. However, Sir W. 

 Thomson himself has greatly weakened the support of this 

 doctrine. But geology (as regards the matter in hand) is not 

 concerned to question it, although it is, at first sight, a difficulty. 

 The results obtained by the Tide Committee of the Association 

 point to the conclusion that there is an i8'6 year-tide in the body 

 of the earth depending on the revolution of the moon's nodes, 

 and that the rigidity of the earth, even if it be in one sense as 

 high as that of steel, is] yet a viscous rigidity, by which she may 

 yield almost indefinitely to sufficiently long-continued straining 

 forces. Other considerations confirm this latter position. This 

 l8*6 year-tide, whether resulting from such viscosity proper or 

 from plasticity of a different kind, imist cause a variation in the 

 earth's rate of rotation during the same period. This variation 

 would probably be desirable if looked for by the astronomers, 

 who would confer a boon on the geologists by endeavouring to 

 detect it. Dr. John Evans' suggestion of the possible considerable 

 mobility of the axis of rotation relatively to the body of the earth, 

 bears in certain ways on the present question ; the mechanical 

 objection to it, already greatly weakened by the Rev. O. Fisher, 

 might be quite i-emovedby the investigation suggested. 



On some New Ere- Cambrian Areas in Wales, by Henry Hicks, 

 M.D., F.G.S. — During some recent researches in Wales the 

 author has been able to add many new areas to the pre-Cambrian 

 rocks already described. In these examinations he has been 

 assisted at different times by Prof. Torrel, of Stockholm, Prof. 

 M=Kenny Hughes, Mr. Tawney, F.G.S., and Dr. Sterry Hunt, 

 of Montreal. The additional areas to be now added to those 

 previously known are : — 



I. Some cupriferous schists with their associated greenstone 

 bands (the so-called intrusive greenstone of the Geological Survey) 



to the north of Dolgelly, and including a great portion of Robel 

 Tawr. 



2. Masses of granitoid rocks, porphyries, and greenstone 

 breccias, in the neighbourhood of Pwllheli. 



3. The porphyries and granitoid rocks forming Myaydd 

 Mynytho, and extending in a northerly direction towards Nevin, 

 including also Nevin mountain and the porphyries and green- 

 stone breccias to the north-east of Boducan. 



4. The Bhos Hirwain syenite and the so-called altered Cam- 

 brian beds to the west of that mass in Caernarvonshire, and also 

 Bardsey Island. 



5. The granitoid rocks, felstones, and porphyries, forming 

 the Rivals (yr Eifl) range of mountains. 



6. The so-called altered Cambrian rocks to the west of the 

 Penygroes porphyry. 



7. The so-called intrusive granite in Anglesea, and the whole 

 of the area marked as altered Cambrian in that island. In 

 addition to these he has also extended some of the areas and 

 defined more clearly the order of superposition of these rocks 

 in Pembrokeshire. In North Wales, as in South Wales, he 

 found that the pre-Cambrian rocks resolved themselves into 

 three well-marked and very distinct types, and that these in- 

 dicated separate formations, each of which, on careful exa- 

 mination, and when found in juxtaposition, proved to be un- 

 conformable to the other. At St. David's the granitoid rocks 

 occur at the base, and, resting unconfonnably upon these, are 

 found the quartz-felsites. These are again succeeded uucon- 

 formably by the agglomerates, breccias, greenstone bands, and 

 schists of the Pebidian group. 



In North Wales this was also exactly the order in which the 

 various rocks were found to succeed each other, but the middle 

 or quartz-felsite group was found more largely develoi^ed in 

 Caernarvonshire. 



As this middle group had not previously been separated under 

 a distinguishing name, the author now proposed to adopt for it 

 the name Arz'onian, from the Roman name Ai-vonia, and from 

 which the present name of Carnarvon is derived. So many of 

 the large ridges and lofty mountains of Carnarvonshire are com- , 

 posed of these felsitic rocks that it appeared to the author and 

 his friends that this name would be very appropriate for the 

 formation. The distinguishing characters most marked in these 

 three pre-Cambrian formations may be briefly summed up as 

 follows : — 



1 . Dimctian : Granitoid gneiss rocks. 



2. Ar-jonian : Quartz, felsites, and porphyries (Halleflinta of 

 Torrel ; petro-silex rocks, Hunt). 



3. Pebidian ; Green and purple agglomerates and breccias, 

 green chloritic schists, with massive greenstone bands, talcose 

 schists. Sec. 



In these formations the bedding is usually easily recognised, 

 but at present the actual stratigraphical thickness cannot be 

 correctly estimated. It is perfectly clear, however, from the 

 sections exposed, that each must have a vertical thickness^ of 

 many thousand feet. That they have a very extended geological 

 distribution over the British islands is also daily becoming more 

 and more evident. 



On the Metamorphic and Intrusive Rocks of Tyrone, by Joseph 

 Nolan, M.R.I. A., &c., of the Geological Survey of Ireland. 

 — The rocks described in this paper occupy the central parts of 

 county Tyrone extending from Omagh eastwards and north-east- 

 wards towards Slieve Gullion. They consist for the most part 

 of an amorphous green homblendic rock, in the midst of which 

 is a wide lenticular tract of micaceous gneiss and schist. The 

 author shows that these two classes pass gradually into each 

 other, and that even among the amorphous homblendic rocks 

 traces of schistose structure can generally be observed, while 

 local transitions into schists frequently occur. Gradations into 

 more crystalline rocks were also noted and described, those of 

 a homblendic character passing into a felspathic variety in which 

 little or no hornblende occurs, while quartz and orthoclase are 

 developed, so that a coarse quartz porphyry is produced, passing 

 iiltimately into granite. 



It was also shown that some of the granite was intrusive 

 during the period of the old red sandstone, a new fact in Irish 

 geology. Its association with metamorphic rocks, probably of 

 lower Silurian age, was explained on the hypothesis that the 

 intrusive granite was due to re-metamorphism of the later 

 period, so that portions of the already crystalline rocks were 

 completely fused and became irruptive. That metamorphic 

 action in this district continued up to and even after the old red 



