188 Mr. Josiah Rees's Application of the Formula 



mentioned. At this point, where the glacier has swept to the 

 westward, and has expanded, its surface seems in a short space 

 to have declined much : for on a hill lying about a quarter of 

 a mile N. W. of the shoulder, and forming a lower part of the 

 same range (it stands S.S.E. of the Victoria Inn, and has a 

 reddish summit), the marks of the passage of the glacier are 

 at a considerably lower level. At the very summit, however, 

 of this hill, several large blocks of rock have been moved from 

 their places, as if the ice had occasionally passed over the 

 summit, but not for periods long enough to have worn it 

 smooth. 



I cannot imagine a more instructive and interesting lesson 

 for any one who wishes (as I did) to learn the effects produced 

 by the passage of glaciers, than to ascend a mountain like one 

 of those south of the upper lake of Llanberis, constituted of 

 the same kind of rock and similarly stratified, from top to 

 bottom. The lower portions consist entirely of convex domes 

 or bosses of naked rock, generally smoothed, but with their 

 steep faces often deeply scored in nearly horizontal lines, and 

 with their summits occasionally crowned by perched boulders 

 of foreign rock. The upper portions, on the other hand, are 

 less naked, and the jagged ends of the slaty rocks project 

 through the turf in irregular hummocks ; no smooth bosses, 

 no scored surfaces, no boulders are to be seen, and this change 

 is effected by an ascent of only a few yards ! So great is the 

 contrast, that any one viewing these mountains from a distance, 

 would in many cases naturally conclude that their bases and 

 their summits were composed of quite different formations. 



XXXI. Application to particular instances of the general 

 Formula for eliminating the Weights of Mixed Bases. By 

 Josiah Rees, Jun., F.G.S., of Her Majesty's Ordnance 

 Geological Survey *. 



HPHE general formula for eliminating the weights of any two 

 •*■ bases, where the whole weight of any particular acid with 

 which they are combined has been previously ascertained, is 

 not easily available to those who are unaccustomed to mathe- 

 matical inquiry. 



If, however, we apply the general rule to particular in- 

 stances, we are enabled to obtain a very simple place for each, 

 by the application of which the weight of the bases may be 

 ascertained. 



I have thought it would not be altogether useless to draw 

 up a few such rules for the use of chemists. 

 * Communicated by the Author. 



