May, 1915. 



KNOWLEDGE. 



151 



sidered in relation to the gradient and discharge of the 

 streams, should indicate the relative duration of the inter- 

 glacial periods. 



Evidence of this nature has been obtained by Rich and 

 Filmer [Jour. Geol. January-February, 1915) in the case of 

 Six-mile Creek in New York State. Numerous moraines, a 

 typically glaciated cross-section, and a floor hanging 450 feet 

 above that of the main valley are certain evidence of the 

 intense glaciation this creek has undergone. In the valley- 

 bottom are three distinct gorges, two of them being pre- 

 glacial and the third postglacial. The earliest gorge is 

 clearly subsequent to the adoption of the U-shape by the 

 valley, but is apparently antecedent to two later glaciations. 

 Hence, it may belong to the first interglacial period. The 

 second gorge, cut in the floor of the first, is later than the 

 ice which filled the latter with drift, but the presence of 

 striae on the walls shows it to be earlier than the third 

 glaciation, so it belongs to the second interglacial period. 

 The third gorge is cut through the material deposited 

 during this last ice-invasion, and there is no evidence of 

 any subsequent ice-action. An alternative explanation is 

 the possibility of an origin by rejuvenation, but there is 

 no evidence of such a process in any of the adjacent streams. 



TRANSPORTATION OF DEBRIS BY RUNNING 

 WATER. — An elaborate account, accompanied by diagrams 

 and tables of data, of numerous experiments on the trans- 

 portation of debris by running water is given by G. K. 

 Gilbert in one of the U.S. Geological Survey publications 

 (Prof. Paper 86). While a considerable amount is known 

 concerning the material carried in suspension by streams. 

 very few facts have been ascertained about the " bed- 

 load " or material swept along the river-bottom. In the 

 experiments described, specific loads of sand and gravel 

 are fed into artificial streams of known discharge, and 

 measurements taken of the effects of the various factors. 

 It is found that for each set of conditions there is a definite 

 gradient below which no load is transported, and that this 

 slope varies with the grain size of material. The variations 

 in the " capacity," i.e., power of transport, due to discharge 

 and grain size are of a lower order of magnitude than those 

 due to slope. The majority of the particles are transported 

 by a process of " saltation," or leaping, though the larger 

 ones show a tendency to roll. With small bed loads, 

 transportation takes place by the down-stream migra- 

 tion of mounds of material, very much like the advance of 

 sand-dunes under aeolian conditions. As the load increases, 

 the surface first becomes smooth, and then " antidunes " 

 form, with an up-stream migration of the crests. Numerous 

 formulae are deduced, but the application of these to actual 

 rivers must be made with extreme care, owing to the great 

 variation, with different conditions of load, discharge, and 

 so forth. 



COMMERCE AMONG THE ESKIMO.- -In the past, 

 trade between the various Eskimo tribes has been con- 

 ditioned by the feasibility of the routes and the resources 

 and distribution of the tribes. The chief highway is the 

 sea, not, however, as water, but as ice. The short season 

 when there is open water is entirely taken up by harvesting 

 and hunting, so that trading is relegated to winter and 

 spring. Until recently, sled journeys from Alaska, even 

 to the Siberian side of the Behring Sea, were common. The 

 chief trading route between the Mackenzie Delta and Hudson 

 Bay lies along the coast as far as (ape Parry, turns north- 

 ward to Nelson Head, and then eastward through Prince 

 Albert Sound, and across Victoria Island. From there it 

 runs due south for three hundred miles to the head of 

 Chesterfield Inlet, and finally down the latter to Hudson 

 Bay. Another route, now disused, keej the coast 



of the mainland, and passes through Coronation Gulf. 

 The speed of such a journey may be judged from the fact 

 that the minimum time necessary for an article from 

 Alaska to reach Hudson Bay is two and a hall years, while 

 the average time is probably nearer five years. The 

 Behring communities transport Siberian goods, such as 



ivory, blubber, and oil. eastward and receive in return 

 skins and stoneware. A full account of the articles which 

 the various tribes deal in is given by Stefansson (Can. Geol. 

 Survey, Museum Bulletin So. 6), and the dependence of 

 these on resources, routes, and so on, is discussed at some 

 length. 



GEOLOGY. 



By G. W. Tyrrell, A.R.C.Sc, F.G.S. 



ORIGIN OF CHINA CLAY.— The origin of this import- 

 ant economic product is dealt with in considerable detail 

 in a Handbook to the Collection of Kaolin, China Clay, and 

 China Stone in the Museum of Practical Geology, written 

 by Dr. J. A. Howe, and published by the Geological Survey. 

 The great West of England occurrences are fully described, 

 along with the methods of obtaining the clay and preparing 

 it for use. Other occurrences at home and abroad are next 

 described. This is followed by chapters dealing with china 

 stone, the uses of china clay and china stone, the mineral 

 kaolinite and its allies, and the various theories of origin 

 that have been propounded from time to time. The last 

 two chapters contain statistics of production and a list of 

 the china clay works of the West of England. An excellent 

 appendix by Mr Allan Dick describes the microscopical 

 characters of kaolin and the delicate methods of investi- 

 gation used for this and similar substances. The hand- 

 book runs to 271 pages, and is an excellent and most interest- 

 ing production 



The principal hypotheses put forward to account for the 

 production of kaolin (mainly from felspars and felspathic 

 rocks) are based on the action of the following agencies : 

 (1) Surface weathering ; (2) waters descending from swamps 

 and bogs ; (3) ascending waters containing carbon dioxide ; 

 (4) emanations following igneous activity ; (5) sulphuric- 

 acid solutions and hydrogen sulphide ; (6) hydro]-. 



The question of origin is of especial interest in con- 

 nection with the rich deposits of the West of England. These 

 arc associated with the great gTanite intrusions of that area 

 especially those of St Austell, Bodmin Moor, and Dartmoor 

 The hypothesis that surface weathering is the chief agent 

 of kaolinisation is the oldest, and still holds pride of place 

 in the textbooks ; but there are niMiperable objections to it 



in the c.ise of the West of England deposits. It is difficult 

 to explain the extremely local distribution "t the kaolin 

 on this hypothesis. One would expect it to be a common 

 and widespread superficial deposit in most granites it it 

 were due to surface weathering. Moreover, gramt 

 quently weathers to considerable depths, but with the 

 formation of materia] very different from china clay The 

 theory which ascribes the origin of the West of England 

 i hin. i clay to the heated gases and liquids accompanying 

 or following igneous intrusion (pneumatolysisi finds much 

 support from the observed facts The localised occurrence 

 oi the kaolin and the fact that the kaolin Ixnhcs appear to 

 become more extensive downwards find ready explanation 

 on this theory Moreover, the kaolin is frequently 

 ciated with topaz, fiuorite, and cassiterite — minerals which 

 are known to have been formed by emanation- containing 

 boric and hydrofluoric a< ids Dr Howe shows that it does 

 not necessarily follow that kaolin is due to the acti 

 these particular ... id- on the lel-pars of the granite, but 

 he. nevertheless, accepts the view that kaolin is due to some 

 kind oi pneumatolytic action, and i- inclined to considei 

 that carbon dioxide, always an important emanation 

 product, i- tin' chief agent in the process. He points out 

 that the operation of tin- factor is not excluded in any ot 

 the described occurrences of kaohn, and is accepted b\ 

 exponents ot all theories alike. It- activity i- recognised 

 in the later phases oi pneumatolysis, in ordinar) weathering 

 and the action of peaty water- in the action of hot or 

 i old spring intaining tin- gas, and also in the process 



ot hydrolysis. 



