96 Dr. J. Croll on the Physical Theory 



said to act in the production of glaciation. They are rather 

 permanent and passive conditions enabling the active causes 

 to produce their required effects. Had the glacial epoch 

 resulted from elevation of the land/ as some geologists sup- 

 pose, then this elevation might properly be said to have been 

 the cause of the glacial epoch ; but the glacial epoch was 

 produced by no such means, nor by any change in the phy- 

 sical geography of the globe. A certain geographical condition 

 of things was, of course, requisite in order to the effective 

 operation of the astronomical and physical causes. This 

 condition existed at the time of the glacial epoch ; and it is 

 only in this sense that that epoch can be referred to any thing 

 geographical. 



It is true that a cause, as Sir William Hamilton states, 

 may be defined as " all that without which the effect would 

 not happen ;" but this is far too general an expression of 

 cause for practical purposes. We therefore fix on the parti- 

 cular antecedent or antecedents, through the activity of which 

 the event is mainly brought about, and term them the causes 

 of the event, and the others the necessary conditions. 



I cannot help thinking that the way in which geogra- 

 phical conditions are spoken of as causes of the glacial epoch 

 has tended to confusion. 



During the glacial epoch there were frequent submergences 

 and elevations of the land, or rather oscillations of sea-level, 

 and these, it is true, would produce a change in the relative 

 extent of sea and land. But whether we suppose it to have 

 been the sea which rose and fell in relation to the land, or the 

 land in relation to the sea, it equally follows that the geo- 

 graphical change resulting therefrom could not possibly have 

 been a cause of the glacial epoch. It is now a well-esta- 

 blished fact that submergence accompanied glaciation ; the 

 glaciation may have been that w T hich led to the submergence ; 

 but it could not possibly have been the submergence which 

 led to the glaciation. An elevation of the land would have 

 favoured glaciation, but submergence would not. Its ten- 

 dency would rather be in the opposite direction. It is now 

 also established, that during the continental period, or period 

 of elevation, the climate was warm and equable ; for it was 

 then, as has been remarked, that this country was invaded by 

 tropical and subtropical animals. Now it is equally plain 

 that the elevation could not have been the cause of the heat. 

 Elevation of the land might produce cold, but it could not 

 have been a cause of the heat. It follows therefore that the 

 geographical change resulting from submergence or elevation 

 of the land cannot be regarded as a cause of the glacial epoch ; 



