GLACIAL ACTION. 35 



tiou east and west. Some other suggestions, however, of this 

 paper have great value those, namely, of a chemical nature, 

 referring to the different degrees of fusibility and rates of 

 cooling among trap rocks, which, if experimentally estab- 

 lished, would elucidate many points still obscure in the 

 natural history of the ancient products of plutonic fires In 

 a later paper, describing the Whiting Bay dikes, Mr. Napier 

 forms a much higher estimate than M. Necker of the total 

 number on the east coast (Trans. Phil. Soc. Glas., vol. iv. 

 p. 321). 



Glacial Action. 



18. Till the publication of the present work, glacial action 

 had not been recognized in Arran ; appearances had, indeed, 

 been observed by Dr. MacCulloch, in regard to scattered 

 blocks and " alluvial mounds," of which the ice theory, not 

 thought of in his day, now offers the best explanation ; but 

 the island had not been examined with the view to discover 

 direct evidences of the action of ice, as in the striation, 

 polishing, and rounding of rocks, the transport of boulders, 

 and the composition and other characters of the superficial 

 accumulations. Some general results of our inquiry will 

 now be stated; details being reserved for the notices regard- 

 ing particular tracts, which will be given farther on. 



The remarkable peak of Cior-Mhor has been already 

 pointed out as the geographical centre of the northern group 

 of mountains (Art. 2). From its base the four great valleys 

 of the island Sannox, Rosa, lorsa, and Eas-an-Bhiorach 

 radiate in all directions, their extremities opening on the 

 seaward belt of low land. If glaciers ever existed in Arran, 

 under the subarctic climate to which Scotland was once sub- 

 jected, these central heights must have been the seat of the 

 snow-fields which fed them, and the radiating valleys the 

 channels down which the viscous mass of glacier ice must 

 have pushed forward to debouch upon the low ground, and 

 melt under a higher temperature. On the sides, then, and 



