14 MR. LYELL ON THE PROOFS OF A GRADUAL RISING OF 



he says, " the position of this lake shows that it has formerly communicated with the 

 sea, though now it is considerably above it and entirely inland. As the sea retired, 

 this sheet of water would also have been drained off, had it not been dammed up at 

 the only outlet (at Alkistan) to preserve the beauty of the promenade, one of the 

 finest in the neighbourhood of the city. At present it is dammed up to the height of 

 four or five feet, and the character of all the land around shows that in ancient times 

 it has been very much higher and more extensive." 



Now a reader would infer from this description, that but for an artificial dam this 

 lake would have been laid dry ; but the fact is that it fills a deep hollow in the granitic 

 rocks of this district ; and the only effect of the small dam is that the mean height 

 of the water is somewhat more uniform throughout the year. The outlet alluded to 

 is at Alkistan (see Map, fig. 7.), where a slight wooden dam has been erected, so 

 small, that every year in the spring the water flows over it ; so that the annual ex- 

 treme height of the water is still the same as it would be if the dam were removed. 

 When I visited the spot in June, the water was two feet lower than the top of the 

 dam, and scarcely more than a foot above the bottom. The tract of land which se- 

 parates the lake from the sea is about a hundred paces broad, and is composed of 

 granite, over which the stream flows which issues from the lake. 



I shall now pass to the country around Upsala, about forty miles north-north-west 

 of that around Stockholm last described (see general Map, Plate I.). In its geologi- 

 cal structure it resembles that of Stockholm, the fundamental rocks being here also 

 gneiss and granite, partially covered with newer deposits and with erratic blocks ; 

 but near Upsala there is a much larger quantity of clay in the overlying formation. 

 A section of this clay is well seen at Ulfva on the banks of Fyrisa, a spot which I 

 visited with Mr. Marklin of Upsala. The thickness of clay here exposed in a vertical 

 section is between thirty and forty feet, and the river is probably as much more above 

 the level of the sea. This stiff blue clay reminded me much of the Subapennine clay 

 of Italy, In some parts it contains no shells; but in others the Tellina Baltica entire, 

 with both its valves and the epidermis, is very abundant. It is precisely the same va- 

 riety of this shell as I found before near Torshalla (see p. 10, and Plate II. figs. 3, 4.). 

 The Mytilus edulis also occurs, often much flattened, and occasionally covered with 

 the small white flustra now so commonly attached to it in the Baltic. In some of 

 the associated strata there is much vegetable matter, exactly resembling sea-weed. 

 I could find none of the littoral shells which I before mentioned as associated with 

 the Mytiltis and Tellina near Stockholm. 



One of those ridges of sand and gravel which I have before described as being 

 frequent in Sweden, passes through the suburbs of Upsala, running in the usual di- 

 rection nearly north and south. Its summit, according to the barometrical measure- 

 ment of Professor Wahlenberg, rises more than a hundred feet above the river which 

 flows at its base. Its structure ia laid open in large pits, one of them about seventy 

 feet deep ; and these sections show that the mass consists for the most part of a con- 



