42 



COURSE OF THE SAP. 



PT. n. 



horse, certainly ! and I am all in the dark about him 

 myself. 



Perhaps the largest blocks of stone ever quarried 

 by man (I do not except Pompey's Pillar for length) 

 are from the granite quarries in Finland. One mode 

 of rending these from their beds was to drill holes 

 along their sides, and to fill these holes with water in a 

 frost. Here ' weak water ' splits the hardest substance 

 by turgescence, or swelling, without a star on its frozen 

 column. This plan was changed to plugging the holes 

 with dry wood, and wetting these plugs simultaneously. 

 Here, again, the mysterious and marvellous power of 

 turgescence performs its Herculean task with apparently 

 very weak implements. A spoonful of water and a 

 email bolt of wood form the blood and frame of a giant 

 who, give him fingerhold, makes a joke of Milo. He 

 changes his name sometimes, though. When he acts 

 on ice, I should have called him dilatation. When he 

 acts by heat, his name is expansion. And to him is 

 confided the growth of geological vegetation. His endo- 

 gens are the Alps, the Himalaya, and the Andes ; his 

 exogens Vesuvius, Etna, and Madeira. Who shall 

 guess from what depths within the earth these last 

 receive their red-hot sap ? But even to raise it after 

 leaving the earth, through the pressure of the Atlantic, 

 perhaps some 30,000 feet, is not a bad squirt. We 

 have then, in the roots and stem, wood and moisture, 

 the implements of turgescence, — a force unhmite.d in 

 power. How to describe the steps by which it is to 



