INDUSTRIAL PROGRESS DURING THE YEAR 1876. ciii 



THEORIES OF GLACIATION. 



The bearing of these observations and conchisions on theories of 

 glaciation is important. While some are content to limit the action 

 of ice to superficial modifications of the surface, others, as is well 

 known, maintain that the grandest valleys and the deepest and 

 broadest lakes have been sculptured by its agency, and that no for- 

 mer distribution of land and water is sufl&cient to explain the extent 

 of the ancient glaciers ; which were ice-caps stretching from the poles 

 to the equator, to explain the existence of which it is necessary to 

 resort to astronomical causes. These causes, according to different 

 theorists, would involve both hemispheres either simultaneously or 

 alternately, giving a succession of glacial periods which, it is claim- 

 ed, can be traced far backward in geologic time. Such views, it is 

 evident, are not easily conciliated with the late observations in the 

 arctic regions, in New Zealand, and in Australia ; and some of our 

 best physicists and astronomers venture to question the soundness 

 of the astronomical hypotheses of this school of glacialists. The 

 marks of a universal ice-sheet should be found all around the globe 

 in the same latitude and at the same levels, while it is well known 

 that glacial phenomena are limited to certain meridians, and that 

 great breadths afford no indications of ice-action. Hence the view 

 of local glaciers of great extent, the origin of which it is possible to 

 explain by geographical causes alone, now finds favor with many, 

 while increasing attention is given to the action of ice-floes and 

 shore-ice. 



There are many problems relating to erosion and the transport of 

 materials which it is attempted to explain by glacial agency, and 

 the question how far this has been operative is now being discuss- 

 ed by many observers, especially in Great Britain. In opposition 

 to the views of Goodchild, who supposes them due to the eroding 

 action of a great ice-sheet. Miller endeavors to show that certain 

 escarpments in Yorkshire must have been pre-glacial, and Mackin- 

 tosh maintains that many of the phenomena referred to ice must 

 have been caused by marine action. Tjdor in the mean time urges, 

 with great ingenuity, that the present surfoce-outlines were deter- 

 mined by the action of water rather than of ice, and would substi- 

 tute for the Glacial a Pluvial period, in which rains, springs, rivers, 

 tides, and currents were tar more active than at present an exag- 

 geration which may be set against those of the other school. 



GLACIERS AS ERODING AGENTS. 



An important question which, it would seem, should take prece- 

 dence of all others in the discussion as to the orifjin and distribution 

 of glaciers or ice-sheets as geological agents, is whether glaciers can 

 act as eroding agents. Bonney furnishes hi3 contribution to the 



