October 22, 1903] 



NATURE 



with a fresh-water layer at its base is thus shown to be 

 between two Boulder-clays, and the committee hopes to carry 

 operations down to the Chalk before the meeting of the 

 Association next year. 



The report of the committee on Irish caves described ex- 

 plorations in some caves at Edenvale, near Ennis. Re- 

 mains of man, associated with those of the bear, reindeer, 

 &c., were recorded. 



Implements, mainly Palaeolithic, from the district 

 between Reading- and Maidenhead were dealt with 

 in a paper by Mr. Llewellyn Treacher. He has 

 obtained them in considerable numbers from gravels at 

 levels of from 60 to 120 feet above the river Thames. The 

 implements are usually of flint, but two examples of imple- 

 ments made from quartzite pebbles were described. The 

 geological history of these pebbles is well known ; they are 

 from the Triassic pebble beds of the Birmingham district, 

 and were brought into the Reading country by the 

 River Thames in an early part of its history, when it 

 drained an extensive tract now within the drainage area 

 of the River Severn. Such pebbles are abundant in the 

 old Thames Gravel, which caps much of the high ground 

 north and north-west of Reading up to a level of about 

 500 feet above the sea, and no doubt the makers of the 

 implements obtained the pebbles from the old Gravel. 



The Swiss geologist, M. Andr^ Delebecque, read a short 

 but very interesting paper on the lakes of the Upper Enga- 

 dine. The lake of St. Moritz is, he said, obviously a rock 

 basin, whilst the lakes of Sils, Silva Plana, and Campfer 

 were, he believed, once a single lake also filling a rock 

 basin. The torrents descending from side-valleys have now 

 partially filled up ^^his basin and divided it into the three 

 lakes. 



This paper led to a discussion on the origin of rock- 

 basins. The author thought that, though Glacial erosion 

 could hardly take place in very compact rocks, yet in many 

 places even granite and gneiss become much decomposed, 

 and glaciers may have swept away the decomposed rock 

 and thus have produced hollows. Mr. Marr considered that 

 every region containing rock-basins must be studied by 

 itself, and that they are probably the result of many different 

 causes. 



Mr. Lamplugh said that, in regions of extreme Glacial 

 erosion, we find true rock-basins near the gathering ground 

 of ice, but as we approach the margin of the glaciated area 

 we find lakes due to terminal moraines, kettle holes, &c. ; 

 thus in the marginal areas the lakes are not the result of 

 direct ice-erosion, but are due to secondary causes. 



.Mr. Clement Reid said it was unfortunate that in north 

 Europe the ice had so completely cleared away the soft 

 deposits of the late pre-Glacial age that we have very 

 little evidence as to the age of the lake or rock-basins. 



In south Europe such evidence is often to be found, and 

 he mentioned a case in Italy, near Florence, where there 

 have been three lakes ; the lowest, now silted up, is of 

 about the age of our Cromer Forest Bed, the second, also 

 filled up, is a Pleistocene lake, whilst the third, and highest, 

 still exists as a lake. The speaker suggested that these 

 lakes were due to earth-movements in a direction at right 

 angles to the valley. 



Passing to petrography, Mr. Teall contributed a most 

 interesting paper on dedolomitisation. Taking a cherty 

 dolomite, such as that of Durness, he showed that it 

 has been dedolomitised by the formation of magnesian 

 silicates, whereas in the case of the marbles formed of 

 calcite and brucite it may be inferred that, under the con- 

 ditions which prevailed during the intrusion of the plutonic 

 rocks, the carbonic acid freed itself more readily from the 

 magnesia than from the lime, thus in the absence of silica 

 giving rise to the formation of periclase and converting 

 the original dolomite into an aggregate of calcite and peri- 

 clase, the periclase having been subsequently changed to 

 brucite. The author instanced the predazzite of the Tyrol 

 as a rock probably formed in this latter way. The history 

 of the rock would then be as follows : — (i) formation of the 

 limestone ; (2) dolomitisation ; (3) intrusion of igneous rock 

 and dedolomitisation in consequence of the development of 

 silicate or periclase ; (4) hydration. 



Mr. G. W. Lamplugh, whose name is well known in 

 connection with the study of crush-breccias and conglomer- 

 ates, read a paper on the disturbances of junction-beds from 

 differential shrinkage and similar local causes during con- 

 NO. 1773. VOL. 68] 



solidation. He thought that in many cases rock was in- 

 durated before it became covered up by the succeeding 

 strata, and that many of the curious structures we see in 

 calcareous rocks may have been due to hardening before 

 anything was laid on top of them. He instanced structures 

 common in the Chalk and Lower Cretaceous rocks. He 

 suggested that shrinkage during consolidation may account 

 for the peculiar appearances which we sometimes see where 

 a thin clay or shale is interbedded with thick sands, such 

 as in the Hastings Sands, or at a junction such as that of 

 the sand of the Lower Greensand with an underlying clay. 



Mr. J. Lomas referred to a similar problem in a paper 

 on Polyzoa as rock-cementing organisms. 



The difficult question of the distinction between intrusive 

 and contemporaneous igneous rocks was raised in papers 

 by Mr. W. S. Boulton and by Messrs. T. H. Cope and 

 J. Lomas, and was discussed at some length. 



Mr. Boulton dealt with the basaltic rock associated with 

 the Carboniferous Limestone at Spring Cove, Weston-super- 

 Mare. The igneous rock shows a marked pillow-structure, 

 contains tuff and agglomerate, and includes lumps and 

 masses of the limestone. 



The tuff within the sheet behaves like a lava showing 

 flow structure, and is clearly not the result of sedimenta- 

 tion. The author believes the included limestone-fragments 

 were derived from the underlying calcareous floor when it 

 was a sea-bottom, the masses having been rolled and picked 

 up by the lava, and thus become intercalated between its- 

 spheroidal masses. He thought the igneous rock was a 

 submarine flow of lava. Messrs. Cope an4 Lomas dealt 

 with the igneous rocks of the Berwyns. The district has 

 a dome-like structure, shales and limestones of Llandeilo 

 age being exposed on the top of the dome, whilst the newer 

 Bala beds form a ring around. There are four thick 

 sheets of rock which have hitherto been regarded as con- 

 temporaneous volcanic ashes. The authors, however, 

 believe them to be intrusive igneous rocks. 



Mr. J. G. Goodchild (Some facts bearing on the origin 

 of eruptive rocks) contended that intrusive masses, as a 

 rule, replace their own volume of the rocks which they 

 invade, and do not cause displacement to any important 

 extent. This paper gave rise to some discussion, for there 

 were present many believers in the existence of laccolites. 

 One speaker suggested that the presence of flow structure 

 along the margins of intrusive igneous rocks was scarcely 

 in harmony with the author's views. It was, however, 

 admitted that there were difficulties when a dyke ends 

 upwards or laterally against strata. 



The palaeontological papers were of considerable interest. 

 Mr. A. C. Seward, president of the botanical section, read 

 a paper before Section C on the fossil floras of South Africa. 

 He considers that the plants from the Uitenhage series of 

 Cape Colony are of Wealden age, and assigns those from 

 the Stormberg Series to the Rhajtic period. With regard 

 to the Vereeniging plants, he describes them as belonging 

 to a flora which flourished in South Africa, India, South 

 .America, and Australia during some portion of the Permo- 

 Carboniferous epoch, perhaps that part nearly correspond- 

 ing to the Upper Carboniferous of Europe. We have, he 

 said, in South Africa as in South America, evidence of an 

 overlapping or commingling of the northern and southern 

 botanical provinces. 



The Carboniferous flora of the Ardwick series of Man- 

 chester was the subject of a paper by Mr. Newell Arber, 

 and some additional details as to the Carboniferous Mollusca 

 were furnished in the report of the committee on life-zones 

 in the rocks of that period. 



Dr. Smith Woodward described an Acanthodian fish, 

 Gyracanthides, from the Carboniferous of Victoria, 

 Australia, and in illustration of another paper he exhibited 

 some fragments of bone from Brazil. They were from a 

 Red Sandstone formation, probably of Triassic age, and 

 it had been suggested that they belong to an Anomodont 

 reptile. 



Mr. W. G. Fearnsides (on the Lower Ordovician rocks..- 

 in the neighbourhood of Snowdon and Llanbcris) gave anj 

 account of his discovery of fossils round the south-wesC 

 and north-west flanks of Snowdon, from Criccieth to 

 Llanberis. They are in beds corresponding to the well- 

 known South Wales Llanvirn series, and are the fin 

 fossils recorded from beds on Snowdon older than t' 

 fossiliferous Bala ash of the summit. 



