114 Lieut. -Colon el Portlock on the Scratching of Bocks 



and then ' enunciated the doctrine that the lateral movement 

 of masses of mud, sand, and gravel, while in a vt^et and plastic 

 state, either under the sea or upon land very recently elevated 

 above it, had been the great agent not only in the almost 

 universal scratchings observable upon the surface of the rocks 

 of every part of the earth, but had been also the means of 

 transport of the far larger proportion of the boulders and 

 greater drift masses that cover the earth.' Mr Mallet 

 showed the close similarity that, in his opinion, exists be- 

 tween the motions, internal and external, of a moving mass 

 of mud or sand and gravel, or of vast landslips, and of those 

 of glaciers ; and at the Cambridge meeting of the British 

 Association, again brought forward his views, adopting the 

 term ' mud glaciers,' as illustrative of this supposed simi- 

 larity." 



It is thus on these gTounds that Mr Mallet claims priority 

 of discovery, and complains that many geologists have 

 adopted his mode of explanation without acknowledging or 

 referring to that priority ; and it becomes necessary, there- 

 fore, that I should set before you so much of the history of 

 this branch of geological science as will be necessary to un- 

 derstand and to decide on this claim. 



It is scarcely necessary that I should here observe, that 

 by early geologists, with some exceptions, the existence of 

 gravel and sand was ascribed to diluvial causes, and that 

 scratches or marks of friction were considered evidence of 

 diluvial currents. In Catcott, for example, the transport of 

 detritic matter by the diluvial stream is strongly urged, and 

 the wear of the strata by diluvial waters. In like manner 

 these effects were ascribed to the movements of water, when 

 Hutton and his pupils Playfair and Sir James Hall, had ad- 

 vanced and illustrated the theories of elevation of mountain 

 masses and marine currents. Mr Greenough (1819), in his 

 critical essays, observes, — " These theories refuted, there 

 remains, in explanation of the phenomena of boulder-stones, 

 the theory which attributes their occurrence, like that of 

 ordinary gravel, to the action of running water. The argu- 

 ments in favour of that doctrine are, that boulder-stones are 

 evidently not in situ ; that they are, for the most part, trace- 



