Boulder Formations and Erratic Blocks. 321 



M. Durocher visited the coasts of Sweden and Norway, in 

 the neighbourhood of Christiania, last year, and discovered 

 there many most remarkable instances of these furrows and 

 strioe, detailed accounts of which he has given in the paper read 

 before the Geological Society of France in December, which I 

 have already alluded to. He, indeed, describes effects of ero- 

 sion on a much greater scale than I remember to have read of 

 before; furrows so deep, that channels are a more appropriate 

 term, as he himself has thought, for he calls them canaux. 

 Both on the east and west coasts of the bay at the head of which 

 Christiania is situated, from Gothenborg on the Swedish shore, 

 and from Arendal on the Norwegian, to Christiania, distances 

 of 160 and 170 miles respectively, and especially among the 

 islands that skirt the Norwegian coast, he observed the i ocks 

 worn into deep channels and furrows, or striated, in directions 

 from north-west to south-east, and having their surfaces round- 

 ed and polished. These channels or furrows are of various di- 

 mensions ; some from twenty-five to fifty centimetres (ten to 

 twenty inches) in width, with a depth of from one and a half 

 to two and three metres (five to ten feet). In a great number 

 of instances, the sides of the interior of these channels are 

 grooved and striated in the direction of their longer axis. 

 Sometimes they divide into two or more branches, which after- 

 wards reunite into one. Many are rectilinear, but many are 

 undulating, and bent in short waves. The axes of the chan- 

 nels and the striae, in their interior, have the same general di- 

 rection as the depressions of the neighbouring country. The 

 north-western extremity of these channels, that is, the open- 

 ings made where the eroding instrument entered, are somewhat 

 wider than the rest of the channel, and are rounded off, po- 

 lished and striated. 



Another very curious, and, as far as I know, a new class of 

 facts has been described by M. Durocher. These furrows, he 

 states, are frequently met with in horizontal lines on the under 

 side of overhanging rocks, and he has met with instances of this 

 description along the Norwegian coast to beyond Drontheim, 

 a distance from Gothenborg of more than 500 miles. One re- 

 markable case he gives, that occurs to the north of Drontheim, 

 where the furrows are cut horizontally in a pudding-stone rock 



