156 Account of the Proceedings of the 



soda diminishes. In the change of the hornblendic into augitic, dial- 

 lagic and hypersthene rocks, there is but little difference in the ele- 

 ments ; the hornblendic rocks are richest in silica and alumina, the 

 augitic in lime and oxide of iron and the diallage and hypersthene 

 rocks in lime, and more especially magnesia. The hornblendic rocks 

 being those which contain most silica, often too much to be altogether 

 combined, form, as it were, the transition fi'om those in which free 

 silica is found, such as granite, to the augitic, diallage, and hypers- 

 thene rocks, where silica is altogether combined with bases. 



M. FrapoUi read a paper on M. Desor's notice of the erratic block 

 phenomena of the north, as compared with those of the Alps, in 

 which he calls attention to the immense quantity of fragments of ice 

 armed with blocks and pebbles, which are driven about the coasts of 

 the north by the storms of winter and spring, grinding against the 

 cliffs and the rocks. The coasts of Scandinavia, he I'emarks, are well 

 known to be encased by a thick coating of ice, which, when broken 

 up carries the blocks and pebbles with it. The masses of block-and- 

 shingle-bearing ice put into motion by the tides and winds range along 

 the shoi'e, polishing and scratching the rocks according to their sur- 

 faces and position ; the cliffs being scratched in horizontal lines along 

 the fiords, and in other similar situations. M. FrapoUi cites a map 

 of M. Weibye of Kragero, upon which the latter has laid down with 

 great precision the scratches and furrows on the rocks of the country 

 bordering the sea in the Bradsbergsamt, and quotes the inference of 

 M. Weibye, " that the scratches and furrows on horizontal, or nearly 

 horizontal surfaces, take a direction always perpendicular to the gene- 

 ral line of coast in open bays, and always parallel to the range of the 

 channels in narrow fiords ; that the horizontality, or the greater or 

 less inclination of the scratches on the inclined or vertical surfaces 

 depends on the relief of the coasts of the locality, and always corre- 

 sponds with this relief, and with the action of different winds." 



From personal observations, M. FrapoUi considers that the scratches 

 and furrows observable in Scandinavia may be referable to the action 

 of ice floated about, always taking into consideration the configura- 

 tion of the coast when the levels of sea and land changed. And cer- 

 tainly the freezing of the sea on coasts, the consequent encasing of 

 blocks and shingles in ice, the drifting of this ice, together with the 

 crushing' and grinding of ice-floes on the coasts, as they are to be 

 found detailed in our voyages to the northern regions of America, 

 are points of importance not to be neglected when we take a general 

 view of the phenomena connected with erratic blocks. Indeed there 

 are cases in our own land where this explanation would accord best 

 with the facts observed. 



In a notice on the Heights of the Jura between the Dole and Re- 

 culet, M. Jules Marcou gives a detailed account of that portion of 

 the Jura range in which its chief heights are included. He observes 

 that the four groups of Jurassic rocks are not exposed on these 



