s26 



NA TURE 



{Sept. 25, 1884 



throw light on many of the practical difficulties hitherto felt in 

 any method of carrying out gyrostatic investigation of the earth's 

 rotation, and which have led the author to fall back upon the 

 method described by him at Southport, of which the essential 

 characteristic is to constrain the frame of the gyrostat in such a 

 manner as to leave it just one degree of freedom to move. The 

 paper concludes with the description of a simplified manner of 

 realising this condition for a gyrostatic compass — that is to say, 

 a gyrostat free to rotate about an axis either rigorously or very 

 approximately vertical. 



Section C — Geology 



On Ice-Ay Theories, by Rev. E. Hill, M.A., F.G.S., Tutor 

 of ?'.. John's College, Cambridge. — On the Montreal Mountain, 

 in I neighbouring quarries, at the mouth of the Saguenay River, 

 an ; more or less everywhere over all Canada and all the north 

 and north-west of this continent, are seen phenomena which 

 imply a former vastly extended action of ice. The like are 

 found over Europe and Asia, thus completely encircling the 

 Pole. Many theories have been propounded to account for 

 these facts. It is proposed to pass these before you in review. 

 Any explanation ought to account not only for cold greater than 

 the present, but for accumulations of snow and ice. A kindred 

 phenomenon is the greater size of the Antarctic ice-cap. The 

 supposed interglacial warm periods, and the unquestioned luxu- 

 riance of Miocene vegetation in Greenland, ought also to find 

 their causes in any thoroughly satisfactory theory. The theories 

 which have been propounded fall into three groups, as Cosmical, 

 Terrestrial, and Astronomical (or Periodical). The Cosmical 

 theories are Poisson's Cold-Space theory — incomprehensible ; 

 and the Cold-Sun theory of S. V. Wood and others — lacking 

 any evidence. The Terrestrial theories are numerous. Lyell's 

 suggestion of Polar-continent and Equatorial-ocean is opposed 

 by evidence that continents and oceans lay on much the same 

 areas as now. The contrary view, Polar-ocean and Equatorial- 

 land, would deserve consideration but for the same opposing 

 evidence. The elevation view (Dana, Wallace), which alleges 

 greater altitude of mountain-chains, disagrees with the strong 

 evidence for land-depression during the period. The submer- 

 gence view of Dr. Dawson agrees with this evidence, but requires 

 elucidation. Alteration of ocean-currents (Gunn, J. S. Gardiner) 

 is a most powerful agency, but would act locally rather than 

 universally round the Pole. Alteration of prevalent winds, 

 hitherto worked out by no one, deserves attentive consideration. 

 Conditions are conceivable which would produce over an area 

 winds from cold quarters almost permanently. However, this 

 seems open to the same objection as the preceding theory. East 

 come the Astronomical or Periodical theories. A tilt of the 

 earth's axis was suggested by Belt, but suggested as owing to 

 causes which are wholly insufficient. Tilting from astronomical 

 agencies is slight, though its action would be in the direction 

 required. Herschel suggested the Eccentricity theory, but aban- 

 doned it. Adhcmar's Precession theory, as explained by him- 

 self, involved an absolute fallacy. The celebrated view of Dr. 

 Croll combines the Precession and Eccentricity theories into one. 

 It exactly agrees with the Antarctic greater extension of ice, and 

 provides an explanation of interglacial warm periods. The great 

 difficulty in its way is to see how a mere difference in distribu- 

 tion through the year of an unchanged total heat-receipt can 

 produce consequences so vast. The laws of radiation explain 

 hut a very minute part, the laws of evaporation perhaps rather 

 more ; but, so far as can at present be seen, both together are 

 inadequate. Another serious objection is that the theory seems 

 to require the climate of the northern hemisphere to be now 

 in a Male of change for the better, of which at present there 

 appears no evidence. Dr. Croll's elaborate explanations of the 

 reaction of one effect upon another— fogs, deflection of currents, 

 and the like — have no special connection with his own theory. 

 They would act in all cases, and support all theories equally. 

 The arguments, if admitted, would only prove that the earth's 

 climates are in a state of highly unstable equilibrium, in which 

 a slight cause may produce an enormous change. Nor are his 

 arguments universally admitted. In conclusion, Dr. Croll's 

 tin cry • ei ms inadequate: alteration of currents and winds are 

 the most powerful causes suggested hitherto: further investiga- 

 tions .-light to be made as to the nature and extent of the last 

 series of changes in the outlines of the continents of the globe. 



What is a Mineral Vein or Lode? by C. Le Neve Foster, 

 B.A., D.Sc, F.G.S., H.M. Inspector of Mines.— The author 



quoted briefly the definitions of a mineral vein given by Werner, 

 Carne, Von Cotta, Grimm, Von Groddeck, Geikie, Sandberger, 

 and Serlo, who, in common with most geologists, have looked 

 upon mineral veins as "the contents of fissures." While ad- 

 mitting that a very large number of veins may be so described, 

 the author contended that the exceptions are sufficiently im- 

 portant and numerous to warrant a change in the definition. He is 

 of opinion that many of the principal and most productive tin-lodes 

 in Cornwall are simply tabular masses of altered granite ad- 

 jacent to fissures ; and he brought forward the opinions of other 

 geologists to show that certain veins in the English Lake district, 

 the Tyrol, Nova Scotia, Nevada, Colorado, California, and 

 Australia, are not fllled-up fissures. In conclusion, he proposed 

 the following definition : " A mineral vein or lode is a tabular 

 mineral mass formed, more or less entirely, subsequently to the 

 inclosing n i< ks." 



77;,? Acadian Basin in American Geology, by L. W. Bailey, 

 Geological Survey of Canada. — The Acadian Basin, embracing 

 the region bordering on and including the Gulf of St. Lawrence, 

 logethei with the provinces of New Brunswick, Nova Scotia, 

 Newfoundland, and Prince Edward Island, constitutes one of 

 the natural physical divisions of the continent of North America, 

 and exhibits many marked peculiarities of climate and floral and 

 fauna] distribution. In its geological structure, and in the 

 history which this reveals, its individuality is not less clearly 

 marked, being often in strong contrast with that of other portions 

 of the continent farther west ; and in some periods and features 

 even exhibiting a closer relationship with the geology of Europe. 

 In the present paper, the facts bearing upon thi-. individuality 

 are summarised and discussed ; including the consideration of 

 the varying land-surfaces of Acadia in different eras, the time 

 and nature of its physical movements, its climate, and its life. 

 A review of recent progress in the investigation of its geological 

 structure is also given. 



['pan the Improbability of the Theory that former Glacial 

 Periodi in the Northern Hemisphere were due to Eccentricity of 

 the Edith's Orbit, ami to its ll'in/.r Perihelion in the North, 

 by W. F. Stanley, F.G.S., F.R.Met.S.— The theory of Dr. 

 Croll, accepted by many geologists, is that former glacial periods 

 in the northern hemisphere were due to greater eccentricity of 

 the earth's orbit, and to this hemisphere being at the time of 

 glaciation in winter perihelion. This theory is supported upon 

 conditions that are stated to rule approximately at the present 

 time in the southern hemisphere, which is assumed to be the 

 colder. Recent researches by Ferrel and Dr. Hann, with the 

 aid of temperature observations taken by the recent Transit of 

 Venus expeditions, have shown that the mean temperature of 

 the southern hemisphere is equal to, if not higher than the 

 northern, the proportions being 15 "4 southern and 15-3 northern. 

 Tl e conditions that rule in the south at the present time are a 

 limited frozen area about the South Pole, not exceeding the 

 sixtieth parallel of latitude ; whereas in the north frozen ground 

 in certain districts, as in Siberia and North-Western Canada, 

 extends beyond the fiftieth parallel ; therefore by comparison the 

 north, as regards the latitude in which ( treat Britain is situated, 

 is at present the most glaciated hemisphere. As it is very diffi- 

 cult to conceive that the earth had at any former period a lower 

 initial temperature, or that the sun possessed less heating power, 

 glaciation in the north could never have depended upon the con- 

 ditions argued in Dr. Croll's theory. The author suggested that 

 glaciation within latitudes between 40° to 60° was probably at 

 all periods a local phenomenon depending upon the direction 

 taken by aerial and oceanic currents ; as, for instance, Green- 

 land is at present glaciated, Norway has a mild climate in the 

 same latitude, the one being situated in the predominating 

 northern Atlantic currents, the other in the southern. Certain 

 physical changes suggested in the distribution of land would 

 reverse these conditions and render Greenland the warmer 

 climate, Norway tire colder. 



On the Occurrence of the Norwegian " Apatitbringer" in 

 Canada, with a few Notes on the Microscopic Characters of some 

 1 aurentian A mphibolites, by Frank I). Adams, M.Ap.Sc, 

 Assistant Chemist and Lithologist to the Geological Survey of 

 Canada. — The paper first gives a short account of the investi- 

 gations which have been made on this amphibole-scapolite rock 

 in Norway, where all the principal deposits of apatite either 

 traverse it or occur in its immediate vicinity. The deposits of 

 apatite in Canada generally occur associated with some variety 

 of highly pyroxenic rock, often holding oithoclase and quartz. 

 The " Apatitbringer " has, however, recently been found in the 



