1854.] 



BRITISH ASSOCIATION FOR THE ADVANCEMENT OF SCIENCE. 



115 



the highest hills remained uncovered by the sea; and when the moun- 

 tains again rose, a set of smaller glaciers was formed. The thickness 

 of the ice in existing Swiss glaciers was known to be very great ; in 

 the Grindelwald it had been ascertained to amount to 700 feet, ami in 

 other instances was probably thicker. The observations of Agassiz and 

 Prof. James Forbes on the height to which grooved and polished sur- 

 faces span up the sides of Alpine valleys, had led to the conclusion, 

 that the ice had once been much more extensive ; and that in the 

 glacier of the Aar, for example, it must have amounted to 2,000 feet. 

 The same method of observation had been applied to North Wales, and 

 it had been ascertained that in the Pass of Llanberris the grooves and 

 roundings of the rocks extended to a height of ],oOO feet above the 

 bottom of the valley. The drifted deposits which overlie these rounded 

 surfaces must have formed during tlie slow depression which followed, 

 and the glaciers must still have existed, since these deposits, though 

 marine, are still of a moraine character. The cold climate continued 

 during the period of depression, and for some time after it; and there 

 was beautiful evidence in the side valleys of the gradual decrease of 

 the glaciers until they died away amongst the higher mountains in the 

 form of morames stretching across the valleys, one within the other. The 

 scratches made by the first set of glaciers passed down the valleys ; 

 those of the smaller glaciers crossed the first obliquely. 



On the Anthracite Deposits, and the Vegetable Remains occurring in the 

 Lower Silurians of the South of Scotland : bg Pbof. H.iRKNKSS. 



These strata form the high land south of the Firths of Forth and 

 Clyde, and have a general inclination to the N.N.W. The highest 

 beds are on the northern side of the range ; and consist, near Girvau, 

 of limestone and sandstone, with fossils of the Llandeilo rocks. To 

 the southward fossils are rare ; but near the lowest part of the series, 

 at Glenkiln, nine miles from Dumfries, organic remains are found in 

 beds of anthracite, resting on 1,500 feet of unfossiliferous purple and 

 grey sandstones and shales. The fossils are Graptolites saggitarius, 

 J)iplograpsus pristis nnd 1>. ramosus : Siphonotreta micula occurs with 

 the Graptolites in a thin bed of black shale at the base of the anlhra- 

 citic beds. At DufF-Kinnel, crustaceans of the genus Dithyrocaris 

 have been found. These fossils do not account for the carbonaceous 

 matter in the black shales, but indications of " fucoids " have been 

 found ; and it is supposed that much of the hydrocarbon of these beds 

 has been lost through the influence of mechanical forces. Fucoids of 

 the genera Palaiochorda and Chondites are found in the ripple-marked 

 flags of a much higher part of the series, north of New Galloway, un- 

 accompanied by anthracite, but associated with a zoophyte (Froto-vir- 

 gularia) and tracks of Annelides. The Anthracite beds were supposed 

 to have derived their carbonaceous matter from sea-weeds floating like 

 the gulf-weed of the present day. 



Prof. Ramsay considered these black schists were of the age of the lower 

 part of the Bala or Llandeilo series. Prof. Forbes remarked that the 

 fossils usually called "fucoids " were rather to be regarded as zoophytes ; 

 and the " Nereites " were believed by German paloeoutologists to be 

 flexible bodies similar to Graptolites and not tracks of Annelides. 



On the Sub-division of the Palaeozoic Rocks of Scotland : by Mk. D. Page. 

 Passing by the oldest systems, the author proceeded to describe the 

 typical developement of the Old Red Sandstone, remarking that the 

 classification of strata should always be founded on the district which 

 exhibited their characters in the higliest degree. The system was 

 considered to extend downwai'ds to the lowest stratum, containing 

 remains of fishes, and to consist of three divisions : — 1. The lowest, or 

 Grey Sandstone series ; 2. The Old Red Sandstone and conglomerate, 

 (par excellence) ; 3. The Yellow Sandstone scries. The spinny-finned 

 fishes (Cheiracanthus, &c.) were most abundant in the lower division; 

 bouy-cased fishes (Cephalaspis, Coccosteus' &c. ) in the middle; and 

 Holoptychii in the upper .series. The "fucoids" were regarded as 

 merely structural peculiarities of the rock ; but according to Dr. Flem- 

 ing, true plants also occurred. The whole system was considered of 

 marine origin, and the conglomerates were believed to have been 

 transported from a great distance by the agency of ice, because the 

 material is not sorted as it would be in a free flowing sea. The Car- 

 boniferous system represented the limestone, mill-stone grit, and coal 

 measures of England ; but in the cast of Scotland there was a peculiar 

 set of sandstones below the carboniferous limestone, called the " calci- 

 ferous sandstone " by JIcLaren, and representing the carboniferous 

 slate of Ireland. These lower coal-measures included also the fresh 

 water limestone of Burdie-house, and numerous beds of trappcan ash; 

 the sandstones were often ripple-marked, and apparently sub-aerial in 



their origin. The beds of coal were not workable, and were asjociated 

 with peculiar fire-clay and shale ; Araucariai were more prevalent than 

 tree-ferns, and Megalichthys and Palsconiscus the characteristic fishes, 

 no shells occurred in the fire-clay, but only in the shales with the fish 

 remains, indicating periodical inundations of the sea. 2. The carbo- 

 niferous limestone was sometimes a very thin band, or several bands, 

 at most amounting to GO or 70 feet ; the associated shales were fully 

 developed, and the whole contained encrinites, retepora;, minute trilo- 

 bites, and other marine fossils, affording even when but a few feet thick 

 an unerring guide to the miner. 3. The millstone grit was very thin, 

 but in some places exactly like the grit of England. 4. True coal- 

 measures, containing a greater variety of coal than in any other field 

 — caking, free-burning, splint, and cannel coal of every variety, besides 

 the "black band," which, if not "coal," passed insensibly into cannel, 

 and was so coaly as to have been interdicted from bein" worked ; 

 "mussel-ban Is" were of frequent occurrence; and there were indica- 

 tions of rapid formation and drift in the fish-scales and sea-shells. The 

 Permian system was not represented in Scotland, unless the " flat coal " 

 of the Fifeshire coast could be regarded in that light. 



Dr. Grifliths remarked, that the term "yellow sandstone" had been 

 already, and long ago, employed_by himself for a lower division of the 

 carboniferous system in Ireland; it was several thousand feet in 

 thickness, and included shales, thin, unworkable coal, and limestone, 

 with marine fossils, all characteristic of the carboniferous system. 



0)1 the Foliation of some Metamorphic Rocks in Scotland: ly Pecfessoe 



E. FOIIEKS. 



It was of great importance to geologists to distingvush between 

 lamination, cleavage, and foliation : the first resulted from original 

 planes of deposition ; the second was a superinduced structure, dividing 

 rocks into lamina; of bedding; thirdly, foliation was the division of a 

 rock into laminte of difl'erent mineral condition. Cleavage had been 

 attributed, by Prof. Sedgwick, its first definer, to electrical action ; by 

 Jlr. Sorby, to a mechanical force ; and by Mr. D. Sharpe, to mechani- 

 cal and chemical influence. The foliation of mica slate, or separation 

 of its mineral constituents into distinct layers, had been attributed to 

 metamorphic action on layers of dilferent constitution ; 5Ir. Darwin 

 had considered it identical with cleavage, and due to the same cause, 

 — the one passing into the other : the same view has been maintained 

 by Jlr. Sharpe. Professor Foi-bes agreed with those who considered 

 it a superinduced structure quite distinct from cleavage or lamination. 

 The author then referred to examples of foliated structure. In a 

 roadside quarry at Crianlarich, near the head of Loch Lomond, where 

 the metamorphic limestone is not distorted, and exhibits distinct lines 

 of bedding, of a pale blue colour, caused by the presence of iron ; also 

 lines of difl'erent mineral matter, the lamina; frequently curved round 

 nuclei; and dark lines of crystils of calcareous spar produced, perhaj f, 

 by the metamorphism of bands and fossils. In the upper part of ibe 

 quarry the limestone becomes foliated with mica, — the foliation being 

 at first parallel with the bedding, then becomes wavy and contorted, is 

 aff'ected by small faults, and contains nuclei of calcareous spar, and at 

 length passes into a mica slate. At Ben Os there is a ealciferous band 

 in the mica slate, which, having the same s'rike with the Crianlarich 

 beds, may eventually prove a guide in unravelling the structure of the 

 country. Two miles from Inveraruon there is a bed of porphyrilic 

 trap in mica slate, and the foliation on the sides of the trap is conform- 

 able. Four miles from Invcrarnon, in a quarry of trap, which sends 

 large and small veins into the mica slate, there is evidence of a second 

 foliation having taken place, following the same veins of trap. Near 

 Tarbert the mica slate is foliated and contorted ; and a bed of calcareous 

 grit cuts through it, without disturbing the relations of the curves and 

 lamina;. In a slate quarry at Lnss, the foliation accords in the main 

 with the cleavage, as observed by .Mr. Sharpe, in the corresponding 

 district ; but whilst the foliation curves round the nuclei of quartz, the 

 cleavage abuts against them. Foliation has also been noticed in tlie 

 baked rocks of Salisbury Crags. Prof. Forbes concluded, ], that fo- 

 liation was a superinduced structure ; 2, that it was distinct from 

 cleavage; 3, that it was not of mechanical origin, but a chemical phe- 

 nomenon ; 4, that it was, perliaps, inducetl by more than one agency. 



Sir C. Lyell remarked, that the Plutonic action, which had changed 

 loose sand into quartz rock, .'^hclls into nn\rble, and day into fcldspathio 

 rocks, had often left the planes of stratification still visible. Tlic un- 

 altered sedimentarj' beds were frequently alTecled by irregularities os 

 great us those of the altered rocks, and by crumplings which it seemed 

 impossible to explain. If these were rendered raclaniorphic, ihero 

 would be danger of attributing to chemical action peculiarities which 

 existed whilst the beds were vet unaltered. 



