214 THE LOCH LOMOND AND OTHER VALLEYS. 



Lomond; consequently, we have a right to assume 

 that the form of the lake-basin is more or less con- 

 nected with the breaks in the underlying strata. Let 

 us suppose a great north-and-south break to have 

 been first formed, with transverse breaks and their 

 accompanying fissures branching from it. Meteoric 

 abrasion, or if under the influence of the sea, marine 

 action, would widen and deepen the fissures or other 

 vacancies that were thus formed ; or if the climate 

 became arctic or alpine, ice would catch up and carry 

 away all loose blocks, forming valleys along the fis- 

 sures and lines of breaks ; while in the broken ground 

 at the crossing or junction of one or more of these lines, 

 the ice would wedge up and bring into the transport- 

 ing power of the glacier all loosened blocks and frag- 

 ments of the rocks, and consequently excavate the 

 rock to a great extent, thus forming the deeps ; then 

 subsequently produced breaks or dislocations would 

 shift the work previously accomplished, and more or 

 less modify it. 



By operations such as those mentioned it seems 

 possible to account for all the phenomena of the basin 

 of Loch Lomond; ice having accomplished the major 

 portion of the excavation along broken lines of rock 

 due to faults and other shrinkage fissures. For the 

 formation of the deep spot due west of the village of 

 Culness a second theory may be propounded ; for 

 when the land was relatively higher, and the deeper 



