LEAA^ES FROM THE ISLE OF MULL, 221 



luxuriant woods in which tlie ArhiUus flourislies and ripens its 



fruit. 



The Mull flora is interesting as supplying fresh confirmation 

 to the view, first propounded by Asa Gray, tliat formerly the 

 entire northern temperate regions possessed a very uniform flora. 

 It was not j)^*^^'^'^^sly demonstrated that the Greenland and 

 North-American Tertiary flora extended to Europe in Eocene 

 times- Its final disappearance from Europe was doubtless 

 due to the causes enumerated by Asa Gray during a Glacial 

 period ; but there must also have been numberless minor migra- 

 tions and changes that will be found to have given local colour- 

 ing to fossil floras, as these are successively brought to light. 

 The flora will acquire a far higher interest when the plants 

 have been studied. The difficulties in determining them are 

 well known, but I trust that care and perseverance will prove 

 them not to be insurmountable. Work in our own country 

 will at best but afibrd us glimpses of the past. The data 

 in regard to the former inhabitants of tlie land are incom- 

 plete and must ever remain so, but wo must not undervalue them 

 on that account. If we really wish to investigate the origin of 

 the existing vegetation of the north temperate world, we shall 

 have to examine tlie enormous scries of plant-deposits iu Spits- 

 bergen, which attain a thickness of some 3000 feet, and were 

 apparently being deposited continuously throughout that critical 

 period when existing dicotyledonous genera were taking shape. 

 If a small vessel could be despatched on an expedition to Spitz- 

 bergen and Greenland, the results of a single summer's collecting 

 would, I believe, far surpass our highest anticipations. 



I desire to express in* conclusion my great acknowlcr 

 to the Duke of Argyll, on whose property the "Leaf Beds" are 

 situated, for assistance rendered, both personally and through 

 his agents; nor must it be forgotten that we might still have 

 been in ignorance of their existence had he not brought them 



into notice. 



