CENTRAL EUROPE. 151 



hence the special considerations of the decrease of moisture in formerly gla- 

 ciated regions will be deferred for the present. A few remarks will, however, 

 be made, at this point, in reference to an interesting fact, namely, the de- 

 crease of the volume of the rivers of Central Europe during the later historic 

 times. 



In some portions of Germany records have been kept for many years of 

 the flow of water in some of the principal rivers, and the question naturally 

 suggested itself, whether a comparison of these records would show that the 

 volume of water passing from 3'ear to year, at various points, had dimini.-hed 

 or increased, or on the other hand remained constant. The eminent geog- 

 rapher, Berghaus, was one of the first to take up this investigation. He 

 worked up the observations of the Rhine made at Emmerich, those of the 

 Elbe at Magdeburg, and those of the Oder at Kiistrin, and came to the con- 

 clusion that each of these rivers had diminished in volume during the past 

 hundred years, and that there was reason to fear that they would eventually 

 disappear from the list of the navigable streams of Germany. 



Later than this, an eminent hydraulic engineer, Gustav Wex, Chief Direc- 

 tor of tlie Donauregulirung, — an important work imdertaken with a view 

 to the regulation and improvement of the channel of the Danube at and 

 near Vienna, — entered upon the same investigation, and in much greater 

 detail. His results, however, are similar in character to those of Berghaus, 

 and seem to demonstrate, beyond possibility of doubt, that the principal 

 streams of Middle Europe, namely, the Danube, the Rhine> the Elbe, the 

 Vistula, and the Oder, together draining an area of 570,000 sqiiare miles, 

 have for many years been carrying a constantly diminishing quantity of 

 water. The longest series used in coming to this conclusion is that of the 

 Elbe at Magdeburg, where the records go back for one hundred and forty- 

 two years ; but the observations for shorter periods of from fifty to seventy 

 3'ears, which in the case of the other streams are all that are available, seem 

 to leave no doubt as to the character of the result.* 



We turn, finally, for evidence of desiccation to the southern counterpart 

 of our own continental mass. Striking as is, in many respects, the resem- 

 blance in orographic structure between North and South America, there is 

 one point in regard to which the diflfeience is ver}' marked. The Cordilleras 

 of North America form a complex of ranges which occupy a very consider- 

 able width, not less than a thou.sand miles in their widest portion, while the 



* See Zeitschrift ties u.st. Ingciiieui" und Aruliitekteu \'iTeiiis, for 1S73. 



