SEPTEMBER 15, 19IO] 



NATURE 



339 



This thickness of ice is equal in weight to about 1600 feet 

 of rock, while the greatest known elevation since the 

 removal of the load is not much more than 700 feet, 

 implying that a weight of 900 feet of rock can be sup- 

 ported by the shield. It may be, however, that in the 

 interior of Labrador, where no beach-lines give evidence as 

 to changes of level, the doming is much greater than the 

 amount suggested. 



It is of interest to note that these adjustments to change 

 of load take thousands of years to accomplish. The rise 

 due to the melting of the Labrador ice-sheet may be 

 going on slowly now, 30,000 or 40,000 years after the load 

 was lifted. 



These sinkings and risings must be accomplished by 

 plastic flow outwards from beneath the loaded area or 

 inward toward the area relieved of its load. 



Instead of a rigid, unyielding shield, we must conceive 

 a stiffly flexible covering over a plastic substratum, where 

 during thousands of years adjustments of level, amounting 

 to hundreds of feet, may take place ; and during millions 

 of years of removal of load by erosion, or of piling on of 

 load through sedimentation, changes of level of thousands 

 of feet can be accomplished. Such changes have taken 

 place on the southern and western sides of the shield with- 

 out any known rupture, while on the east the adjustment 

 has been accomplished in part by great faults. 



Has the .Archaean, which is supposed to underlie the 

 stratified rocks in all parts of the world, undergone the 

 same vicissitudes? 



Sninmary . 



The history of the Canadian Shield begins in pre- 

 Keewatin times, with land surfaces on which weathering 

 took place, and seas in which mud and sand were 

 deposited. If the earth were ever molten, that stage had 

 long been passed before the Keewatin sediments were laid 

 down, for they include carbon, probably derived from 

 fucoids, which could not have lived in a hot sea. 



The pre-Keewatin land surfaces and sea bottoms have 

 totally disappeared, so far as known to Canadian geology. 

 . Apparently they have been fused and transformed into the 

 gneisses of the Laurentian. 



The Keewatin was a time of great volcanic activity, 

 lava streams and ash rocks surpassing in amount the thick 

 sheets of sediments. -At the end of the Keewatin the 

 thousands of feet of volcanic and clastic rocks were lifted 

 as domes by the up-welling of batholiths of early 

 Laurentian gneiss. 



Then followed a profound gap in the record, during 

 which the mountains were levelled to a hummocky pene- 

 plain. This gap represents a very long period of weather- 

 ing and destruction on a land surface, ending in glacial 

 action on a large scale. 



The Lower Huronian begins with the deposit of a thick 

 and widespread Boulder Clay, followed up by a trans- 

 gression of the sea in which mud and sand, and also lime- 

 stone and chert, were deposited. 



After a short break similar processes went on in the 

 Middle Huronian. During the Middle Huronian, or in 

 the interval between it and the Upper Huronian (.Animikie), 

 mountain-building was renewed on a grand scale, many 

 synclines of Keewatin and Lower Huronian rocks being 

 ■caught between the rising batholiths of late Laurentian 

 gneiss. \ broad central band of the Lower Huronian 

 escaped this process, however, and has preserved its 

 original attitu^le on a floor of Keewatin and Laurentian. 



The .^nimikie or Upper Huronian sediments which rest 

 on the planed-down floor of upturned Lower Huronian, 

 Laurentian, and Keewatin rocks, consist largelv of chert 

 and carbonaceous slate or shale, which lie nearly hori- 

 zontal and have undergone verv little change. 



The Keweenawan follows the Animikie with onlv a 

 small break, and includes shallow water-beds of sandstone 

 and conglomerate, accompanied by immense outflows of 

 lava. .As a result of the outixiuring of lava, great basins, 

 like that of Superior, resulted. It is probable that during 

 the -Animikie and Keweenawan most or all of the Canadian 

 Shield was covered by the sea. 



The Keweenawan is gene^rally held to mark the close of 

 the .Archaean (or .Algonkian or Proterozoic). Low reports 

 portions of these formations as having been caught in 



NO. 2133, VOL. 84] 



mountain-building of the Laurentian type in Labrador, but 

 commonly they have not been disturbed. 



During early Palaeozoic times the Canadian Shield was 

 more than once encroached upon by the sea; though prob- 

 ably much of the peninsula of Labrador, and perhaps a 

 region north-west of Hudson Bay, escaped. 



From the Devonian to the Pleistocene the shield seems 

 to have remained dry land, and part of the Ordovician 

 and Silurian capping of sediments was removed during 

 this long period. 



The succession of Pleistocene ice-sheets completed the 

 work of denudation, and at the end of the Ice Age many 

 thousands of square miles of the lower portions were once 

 more beneath the sea. 



Last of all, the region has been rising at unequal rates 

 in different parts, as shown by the warping of marine 

 and fresh-water beaches. 



The surface of low hills and rounded knolls of gneiss 

 and schists beneath the Pleistocene Boulder Clay resembles 

 in every way that beneath the flat shales and limestones 

 of the early Palaozoic, or the nearly horizontal sediments 

 of the .Animikie, or even the undisturbed parts of the 

 Lower Huronian Boulder Clay. It may be that much of 

 the surface has been covered with sediments and restored 

 to daylight by subaerial erosion several times in succession. 

 The greater part of the carving-down seems to have been 

 done before the Animikie — i.e. within pre-Cambrian times 

 — and the pre-Huronian surface seems as mature as any of 

 the later ones. The bearing of this on the length of early 

 geological time is evident. Pre-Huronian time includes 

 the laying down of thousands of feet of Keewatin sedi- 

 ments, the elevation of early Laurentian mountains, and 

 the levelling of these mountains to a peneplain. It may 

 be as long as post-Huronian time. 



Prof. F. W. Dyson, F.R.S., Astronomer Royal for 

 Scotland, has been appointed Astronomer Royal in 

 succession to Sir William Christie, K.C.B., F.R.S., who 

 is to retire on October i. 



-At the age of seventy-eight years, and in his native 

 place, Lunel, Eugene Rouch^, the well-known mathe- 

 matician, recently passed away. He entered the Ecole 

 Polytechnique in 1852, and on completing his course there 

 devoted himself to teaching, in which he was very 

 successful, and the composition of text-books, which 

 quickly obtained a high and deserved reputation. The 

 treatise on geometry which he wrote in partnership with 

 Charles de Comberousse may be fairly called a classic, and 

 is an excellent example of what such a work ought to be ; 

 many teachers in this country must have found it a most 

 useful source to draw upon, both for theorems and for 

 examples. Engrossed as he was by these occupations, 

 Rouch^ found time to write a number of original notes 

 and papers, and his talents received fitting recognition in 

 1896, when he was elected a free member of the French 

 Academy of Sciences in succession to Baron Larrey. 

 Friends who knew him intimately bear witness to his 

 personal charm and vivacity, and the academy, on 

 August 22, passed a vote of sympathy with his widow and 

 family, after hearing a brief account of his career from 

 the president, M. Emile Picard. 



Is the death, in his seventy-seventh year, of Prof. 

 Friedrich von Recklinghausen, of Strassburg, pathologv 

 loses one of its most distinguished investigators. Working 

 along the lines marked out by Rokitansky and Virchow, 

 V. Recklinghausen played a conspicuous part in building 

 up our knowledge of pathological anatomy during the second 

 half of the nineteenth century. His researches threw a 

 great deal of light upon many aspects of disease of the 

 circulatory system, especially the phenomena of thrombosis 



