Professor T. G. Bonney — Lake-hasins in the Alps. 15 



But one of the most remarkable features of the " Bothnian 

 schists " in the neighbourhood of Tamraerfors is the presence of 

 conglomerates on several horizons. These, in many instances, are 

 so fresh that one finds some difficulty at first in believing that they 

 are really Archaean. The waves of Lake Nasijarvi, in the lovely 

 bay of Hormistonlahti, where these conglomerates are well exposed, 

 have assisted the atmosphere in picking out the more or less 

 crystalline cement between the pebljles. In other situations these 

 Finnish rocks reminded me strongly of certain Cambrian 

 conglomerates in North Wales ; but I do not desire to draw the 

 comparison any closer, for the Cambrian of the neighbouring parts 

 of Russia, as everyone knows, is peculiar, as being so little affected 

 by the ravages of time. 



Mr. Sederholm places^ the thickness of the Tammerfors schists 

 at from 4,000 to 5,000 metres — 2,000 metres for the phyllades, 

 1,500 for the lower tuffs and conglomerates, and the remainder for 

 the upper tuffs with their intercalations of phyllade and con- 

 glomerate. 



The Post-Bothnian granite, which crops out to the north of the 

 schists in the Tammerfors area, is shown by Sederholm to traverse 

 the latter, veins being thrown out at certain places, and large pieces 

 of the schists being caught up at frequent points along the junction 

 between the two rocks. And these pieces of included rock, in 

 addition to possessing the structure and mineral composition of the 

 Tammerfors schists, have occasionally been discovered to contain 

 typical pebbles as found in the last-mentioned formation. 



As I proceed with the narrative, I propose to give field notes 

 and some account of the micro-structure of examples of these 

 Archasan rocks which I collected, and to deal with the Glacial 

 deposits, in the next article. 



[To be continued.) 



IV. — Notes on some small Lake-basins in the Lepontine Alps. 

 By Prof. T. G. Bonnet, D.Sc, LL.D., F.R.S., V.P.G.S. 



ROCK-BASINS have been getting out of favour of late. The 

 " heckling " which they have suffered from my friend 

 Mr. Marr tempts one to echo Betsy Prig's classic remark about 

 Mrs. Harris. Mr. Brend, however, though " dealing faithfully " 

 with them in the September number of the Geological Magazine, 

 does permit one or two to exist on sufferance, so that I feel minded, 

 were it only as an act of charity to these depi-eciated securities, to 

 describe two or three examples in the Alps which I think must be 

 true rock-basins. 



The first is called the Lago Treraorgio.^ It lies, at a height of 

 5,997 feet above the sea, on the southern flank of the Val Bedretto, 

 at the top of a long and steep ascent from Fiesso. It is slightly 

 irregular in outline, but circular in form, with a diameter between 



1 Op. cit. supra, p. 4. 



2 I examined it in 1893. 



