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GEOLOGICAL MEMOIRS. 



ranges, although the altitude of this limit may itself somewhat vary. 

 We may take 3*5° C. as the mean temperature. Immediately above 

 the limit of arboreal growth we remark the most sudden diminution 

 of the ground-temperature, and the most marked differences between 

 the various springs ; — 7. The springs in valleys are, at equal heights, 

 warmer than those on the declivities and summits, and this is stri- 

 kingly perceptible in the higher regions. In like manner, owing to the 

 greater radiation from isolated rock-masses, a remarkable depression 

 of the ground-temperature takes place in the limestone Alps on the 

 free declivities towards the north; — 8. The minimum temperature of 

 the highest springs in the Alps appears to be 0*8° C. ; — 9. The height 

 of the mountain-ranges has considerable influence on the ground- 

 temperature. We find at equal altitudes above the sea-level the 

 warmer springs where the mean elevation is greater ; the isogeo- 

 thermal lines are thereby subjected to curvatures analogous to those 

 of the lines of elevation in the district. These curvatures are shown 

 in a diagram representing a section of the Alps. The numerical 

 results of the numerous observations (given in a tabulated form at 

 pp. 269-273), made with reference to the temperature of the iUpine 

 springs and the isogeothermal conditions of these mountains, are 

 expressed in the accompanying table (see opposite page). 



The Changes effected on the ear tK s surface bij Erosion andWeather- 

 ing are considered by M. Adolph Schlagintweit, in the twelfth chapter 

 (pp. 274-316). The Hydrographical conditions of the Alps are first 

 insisted upon. The mass and annual distribution of the Alpine 

 waters is noticed, also the determinations of the quantity of water 

 flowing from glaciers, illustrated by a table. The temperatures of 

 the Alpine lakes, springs, brooks, and rivers, the rapidity of flowing 

 water, with a table, and the powers of suspension and solution exercised 

 by the waters of the Alps, also accompanied by tables, are copiously 

 treated of. With regard to the quantity of matter suspended in 

 water, there is considerable variation in different seasons of the year, 

 and the quantity is always considerably increased by heavy rains and 

 falls of snow. It is important to notice the great quantity of matter 

 suspended by glacier-streams. This is occasioned by the water, pro- 

 duced by the thawing of the surface, having no definite channel at 

 the bottom of the glacier, and forming a great number of little streams 

 that deposit a quantity of finely triturated rock-substance between the 

 ice and the underlying surface. By the friction of this sand and the ice 

 on the floor beneath, fresh detrited material is always being produced 

 for the brooks. 



According to Dollfuss the water of the Aar near its exit from the 

 glacier contains 142 grammes of suspended matter in a cubic metre. 



Besides detrital matter held in suspension, water in every instance 

 contains certain constituents that have been dissolved by it. These 

 are very various, both quantitatively and qualitatively, in the different 

 rivers, and are connected with the general geognostical conditions of 

 the different districts. The glaciers in high regions are of course far 

 poorer in soluble matters than the Rhine and Aar. The substance 

 most abundantly held in solution is carbonate of lime. A quantita- 



