THURSO RIVER. 159 



interest. He visited every locality in Caithness where 

 boulder clay existed. He went as far as John o' Groat's 

 and Freswick in one direction ; and to Dunbeath, at the 

 southern limits of the county, in the other. He did the 

 most of his journeys at night ; sometimes walking in the 

 dark, at other times in bright moonlight. He seems Jo 

 have been intensely interested in all that he did. Every- 

 thing was to him new and wonderful. His delight was 

 often like that of a thoughtful child, in seeing further 

 into the mysteries of a piece of fine mechanism. 



"It appears to me," he said in a letter to Hugh 

 Miller (1st September 1848), "that the best way of 

 answering your queries, will be to relate in a plain and 

 simple way the various truths which have dawned upon 

 my astonished mind, during my rambles of the last few 

 weeks. 



" Few are acquainted with the peculiar features of 

 Thurso river. Few are aware that, in many places, as it 

 nears the sea, it has scooped out its course deep in the 

 blue boulder clay. Near the town, on the west or left 

 bank, a bed of this blue clay is seen within a stone's cast 

 of the bridge. On the east you see it at Mill Bank ; and 

 on both sides, after that, an immense mass runs on, 

 almost continuously, four miles inland, until at Todholes 

 it becomes low, and on a level with the surrounding 

 fields. Throughout its whole extent it almost invariably 

 presents the same characteristic marks pieces of blue 

 stones, granite, gneiss, and such like. 



" Not long since, the Thurso East Salmon Fishing 

 Company ran a dyke or wall across the river ; and ID 



