276 PROCEEDINGS OF THE COTTESWOLD CLUB 



deep-seated spring, and not from any surface drainage 

 which would aftbrd an intermittent and very variable 

 supply in summer and winter, drought and snow-time. 

 The source of heat is probably constant in all cases, and 

 the intervals between eruptions depend on the size of the 

 reservoir and the quantity of water which enters it in a 

 given time. 



I have now brought you to the head of the Firehole 

 Valley; and I should gladly, if the time had allowed, have 

 crossed the great "Divide" or "Water-parting," which runs 

 along the E. side of the V'alley, and visited the fine 

 sheet of water called the Yellowstone Lake, from which 

 the Yellowstone River flows northwards through a mag- 

 nificent caiion, [lantern slide shown,] forming falls more 

 than twice as high as those of Niagara (350 feet, by line 

 measurement), though not quite equal to the latter in 

 volume. This " Grand Canon," as it is termed, is one 

 of the finest examples of river erosion in the world. 

 [Lantern slide shown.] It is 20 miles in length, 

 and averages about 1,000 feet in depth, and the same in 

 width. The sides are not perpendicular as in some of 

 the Colorado Caiions, but slope at an angle of about 30*^ 

 from the vertical. Standing out from the sides there are 

 numbers of rocky masses, like the "Seven Sisters" at 

 Symond's Yat, carved by weather action into the most 

 fantastic forms, — pillars, watch-towers, buttresses, pin- 

 nacles, all glowing in the sunlight with varied tints of 

 yellow, orange, and red, from the quantity of iron oxide 

 which the trachyte contains. The river has, in fact, cut 

 its way through two distinct lava sheets, one overlying 

 the other ; its work being rendered easier by the disinteg- 

 rating action of the steam and boiling water from the 

 numerous hot si)rings which gush out from the sides of 

 the chasm. Its course of destructive erosion was arrested 

 by an immense vertical basaltic dvke, which crosses the 

 canon diagonally at the Falls, and forms a barrier like a 



