302 Mr. J. Orton on the Evidence of 



like a sheet the whole countiy (plains, campos, and sierras), 

 is drift, the product of a general glacier*. It is doubtful if 

 even local glaciers, of any great extent, existed on the moun- 

 tains of Minas when they stood at a higher altitude than at 

 present, for tlie same reason that glaciers are now absent from 

 the equatorial Andes ; but, for arguments already given and 

 to follow, we certainly cannot believe in the existence of a 

 vast glacier stretching from the Andes to the Atlantic. 



3. We question the possibility of its formation. At the 

 equator there is little variation of temperature. Pard is noted 

 for its equable climate, varying little from 80°. At the Ha- 

 cienda, on the slope of Antisana, 13,300 feet, the mean tem- 

 perature in spring is 42°, summer 38°, autumn 40°, ■s\-inter 41°. 

 The snow-line on the equatorial mountains is therefore sta- 

 tionary ; while the oscillation from summer heat to winter 

 cold, in northern latitudes, gives rise to a variable snow-line- 

 in the Alps, the variation, from January to July, is 34°. 

 Now the snow-line at the equator remains throughout the 

 year at 15,800 feet ; at the latitude of New York it is only 

 one lialf of this. Therefore, to bring the snow-limit down to 

 sea-level would require excessive coldf- But this more than 

 polar reduction of temperatm'e, and the unifonii climate, would 

 destroy the conditions necessaiy for the manufacture of the 

 glacier, which must be constantly fed ; and tlie supply de- 

 pends on an abundant snow-fall, and this, again, on humidity. 

 But an intense unchanging Avintcr would be a diy one. Be- 

 sides, if a snow-field does not attain a temperature higher than 

 zero, it can never become a glacier ; for the particles are as 

 incoherent as sand J. 



Moreover, if formed, we doubt its abilit}' to move. The 

 extraordinary unbroken winter would prevent all movement ; 

 for this depends on repeated accumulations of snow and ice at 

 tlie high sources, and on a change of seasons. All theories 

 of glacier movement arc based on the periodical partial lique- 

 faction of the surface. The Alpine glaciers move twice as 

 rapidly in summer as in Avinter. Then, too, the slope is in- 

 sufficient. Forbes Says a glacier must have an angle of 3° or 



* Rounded and angular quartz-pebbles cemented with ferruginous 

 loam are seen in the Pebiis district. 



t In Europe the most southern glacier which comes down to the sea 

 is on the coast of Norway, lat 67^. 



X According to Hopkins, if blocks on tlie Jura were transported from 

 the Alps bv the agency of ic(>, the Alps must have boon at least (KXX) feet 

 higlior than at prosont. But the lower the latitude, the higher the ole- 

 vation 'iioodod. Wiio will estimate the altitude necessary to send an 

 Andean glacier to the Atlantic ? 



