103 



KNOWLEDGE. 



March, 1911. 



abundant in the abysses. Where sunlight and green plants 

 are wanting no organic life can be maintained ; the fauna of 

 the deep sea is dependent upon the stream of cold south polar 

 water pouring oxygen and food into its abyssal depths. TIic 

 origin of this fauna nuisf. then, he sought in sunlit areas 

 rich in plants. When did the peophng of the abysses take 

 place ? The significant fact appears that no single Palaeozoic 

 animal is found in the present deep sea, although a number of 

 shallow-sea and other genera survi\e from the Palaeozoic Era 

 (e.g. Lingula, Mytilus, Pleurotomaria. Nautilus, Serpula, Astro- 

 pecten, the littoral Liinulus and the fluviatile Ceratodus, 

 besides soft-bodied animals which could not be preserved 

 fossil). Animals nowh\ ing below two thousand metres date only 

 from the Trias, the resemblance to Jurassic and Cretaceous 

 faunas being particularly close ; among the Echinoderms, for 

 example, are found Pentacrinus, Asterias, Echinus, etc. 

 Evidently, then, the peopling of the deep sea is traceable. 

 at the earliest, to the Triassic Period. 



Now we know that the elevation of mountain-chains is 

 counterbalanced by the formation of extensive depressions ; 

 also that at no other period did such enormous mountain 

 folding occur as took place between Carboniferous and 

 Triassic times, when the Hercynian movements in Europe 

 occurred, the Appalachians were formed in America, the 

 Sudanese mountains were originated in Africa, and other 

 folding took place in Asia and elsewhere. /;; the deep ocean 

 abysses Dr. Walther sees the complementary depressions 

 to these mountain chains. 



Thus general biological grounds, the stratigraphical position 

 of the present deep sea fauna, as well as tectonic investigation, 

 force us to the conclusion that the deep sea as a life-region is 

 not a characteristic of the Earth in its oldest periods, and 

 that its origin is found in the time when in all parts of the 

 present continents began tectonic folding movements which so 

 decidedly changed the relief of the Earth's surface. 



THE GREAT NEW ZEALAND ERCPTION.— In the 

 January number of the Geographicitl Journal Professor 

 James Park describes the volcanic outburst of Mount Tarawera. 

 which took place in 1885. and which utterly destroyed the 

 celebrated pink and white terraces of Rotomahana. The 

 subsequent changes due to waning vulcanicity and to 

 denudation are also dealt with. Mount Tarawera — three 

 thousand six hundred feet high — rises abruptly from the lofty 

 rhyolitic plateau of Rotomahana. in the North Island of New 

 Zealand. During a space of about three hours the mountain 

 was gradually rent across from north to south by a great fissure, 

 nearly nine miles long, averaging two hundred \-ards wide and 

 from one hundred to three hundred yards deep. The \ulcanism 

 was of a. rare or new type; for whereas fissure eruptions are 

 distinguished by quiet emission of lava-floods, in this case the 

 ejecta were almost entirely fragmental, consisting of dust, 

 lapilli, bombs, and so on, derived from an augite-andesite 

 magma, intermixed with some rhyolitic ash. These materials 

 were spread over an area of nearly six thousand square miles, 

 in a sheet varying up to fifty feet in thickness, and dust fell on 

 vessels one hundred and fifty miles away. This great ash 

 sheet has since become covered with dense jungle, and has been 

 deeply scored by rain into narrow gutters and ridges. The 

 sections thus exposed are seen to consist of grey dust and 

 black ash, so well stratified as to be easily mistaken for a 

 subaqueous tuff. 



During the course of the fissuring Lake Rotomahana was 

 encountered, and as a result a shattering explosion converted 

 the lake-bed into an active volcano o\er a mile in width. .A 

 native village on its shores was simply blown out of existence, 

 all the inhabitants being instantly killed. Several other 

 villages were overwhelmed with dust, not a soul surviving. 

 For a few months violent hydrothermal activity was displayed, 

 a pillar of steam rising to over fifteen thousand feet ; it then 

 waned and ceased, and the lake-bed filled up again with water. 

 About 1897, geysirs again began to play and the world-famed 

 Waimangu geysir was in action until two or three years ago. 

 Though this has now ceased, solfataric action is still very 

 conspicuous on the lake-shores. At Echo crater the forma- 

 tion of iron pyrites can now be seen in progress ; the crater- 



floor is covered with a thin sihceous crust, through which 

 boiling water and steam escape. Interaction takes place 

 between the hot ascending mineralised waters, and the HoS 

 with which the steam is charged, and as a result FeSo is 

 deposited, first as a black and then a bright yellow film on all 

 the loose stones lying around. 



Though of an abnormal type, the 1886 eruption was merely 

 one of a long succession of volcanic phenomena which have 

 been in progress since Pliocene times along the great tectonic 

 fracture known as the Whakatane fault — along which are 

 situated many other volcanoes, active, dormant and extinct. 



GEOTECTONIC SYMMETRY.— Last November there 

 appeared in these columns a note dealing with the " Canadian 

 Shield." a great mass of gneiss and schist forming one of the 

 ■' corner stones '" of the earth. In the American Journal of 

 Science for December R. Ruedeman points out the strikingly 

 symmetrical arrangement of the large area of Palaeozoic 

 rocks, which extends southwards from this Canadian 

 " protaxis," or shield of pre- Palaeozoic rocks. This area, the 

 '■ Palaeozoic Platform" of North America, is roughly bounded 

 on the west by a line connecting the head of Lake Superior 

 with the Ozarks, and on the east by a line enclosing the 

 .^dirondacks and Appalachians. It corresponds in its relation 

 to the Canadian shield with that of the Russian platform to 

 the Baltic shield. It is bounded on the west by the trans- 

 continental depression occupied by Cretaceous and Tertiary 

 rocks. 



On either side of the Canadian shield there stand out, 

 like a corner-stone, a pre-Cambrian area (" Isle Wisconsin " 

 and " Isle Adirondack"), in quite symmetrical positions. 

 From each of these extensions there runs outward, along 

 the margin of the shield, a deep depression, the Lake 

 Superior basin and the St. Lawrence basin, respectively. 

 From these same corner-stones there extend southwards a 

 pair of arms, as it were, each consisting of a broad belt of 

 pre-Cambrian and early Palaeozoic rocks, nearly the full 

 length of the Continent. In both cases this elevated tract of 

 old rocks terminates to the south in a pre-Cambrian mass, 

 and these two masses — " Isle Ozark," on the west, and " Isle 

 Appalachia," on the east — are symmetrically situated. 



Thus is enclosed a great median basin (that of the Great 

 Lakes and Ohio) which is itself symmetrically sub-divided by 

 the Cincinnati geanticline. This broad anticline, striking 

 north and south, separates two sub-basins of younger 

 Palaeozoic strata, situated in symmetrical east and west 

 positions : it dies away to the north, being replaced by the 

 Michigan basin. In this basin we may, perhaps, see a result 

 of a longitudinal oscillation of the axis of the Cincinnati 

 geanticline, for it also lies symmetrically to the whole arrange- 

 ment, constituting, with the Cincinnati uplift, the axis of 

 symmetry of the whole " Palaeozoic Platform." 



One serious disturbance of symmetry has occurred, due to 

 Atlantic pressure exerted from the south-east ; this has 

 pushed the eastern arm inwards, thus giving rise to the 

 Appalachian basin-folds. Even here, however, the belt of old 

 rocks is recognizable, running south and south-west from New 

 York as far as Alabama. 



MKTI-OROLOCA'. 



By John A. Curtis. F.R.Met.Soc. 



The weather of the week ended January 21st was, generally 

 speaking, dry but dull, with a good deal of fog. Temperature 

 was above the average in Scotland and in Ireland N., but 

 below it elsewhere. The highest readings were 53 at 

 Killarney and Scilly on the 16th, while the lowest readings 

 were 21' at Swarraton on the 15th, and at Durham on the 

 21st. In Scotland N. and the English Ch.annel. the lowest 

 readings were 35', but in all the other districts frost was 

 recorded, from 28° downwards. The lowest readings on the 

 grass were 15° at Crathes and Llangammarch Wells, and 16° 

 at Durham and Kew. Rainfall was deficient in all parts and 

 in most districts markedly so ; at many stations no rain was 

 reported during the week. In Scotland N., however, there 

 were stations where rain fell each day, though not to excess. 



