294 Prof. A. C. Ramsay on the Glacial Theory of Lake-Basins. 



Lago Maggiore from end to end is about thirty- 

 three miles long, if we disregard the curve of 

 the lake, and from its efflux to the Borromean 

 Isles, where it is deepest, is twelve or thirteen 

 miles, and the average upward slope of the 

 bottom of the lake to its outflow from that 

 point is about 2° 21'. If, then, the chief line 

 of depression lay in the centre of the Alps, 

 and if that depression was the cause of the 

 formation of the lake, then it is evident that, 

 before the bottom of the lake assumed its 

 present form, the whole region, from its out- 

 flow to the centre of the Alps, must have 

 been so tilted, that the present upward slope 

 from the Borromean Isles to the efflux must 

 have sloped the other way (viz. south) at some 

 angle, however small. And here I must have 

 recourse to a diagram ; for experience has shown 

 me that many admirable geologists are yet ex- 

 ceedingly apt to exaggerate or else to neglect 

 their angles. It is, as near as may be, on a true 

 scale. Let a be the crest of the Alps, say 14,000 

 feet high, b the northern end of the lake, c 

 its bottom, 2625 feet deep, d its efflux, and bdc 

 an angle of 2° 21', viz. the slope of the lake 

 from c to d. What we have got to do is to 

 alter the general levels of the country by a 

 maximum upheaval at a, so that the line c d, 

 instead of sloping upwards from c to d, shall 

 slope downwards a little in the opposite direc- 

 tion, viz. from e to d. The depth at c e is 2625 

 feet ; and to give the argument every point 

 against me, let the axis of the movement lie 

 at d. There the actual movement will be nil', 

 and for every mile you proceed towards a the 

 amount of upheaval will increase. To restore 

 the country to its original form, as supposed 

 by Sir Charles, let the point c be raised 2625 

 feet because of a general tilt of the solid coun- 

 try comprised between the lines a d cf, so as 

 to raise the triangle bed into the position of 

 the triangle g e d. Then it so happens that / 

 the line df at f will be raised as near as may 4' 

 be to the point a ; or, in other words, the crest \ 

 of the Alps would be raised to h, and the whole 

 range in this neighbourhood, at the period 



