28 ECONOMICS OF FORESTRY. 



given new and constantly growing employment to 

 wood. 



Considering, moreover, the very extensive and the 

 very varied employment of wood, it will be appar- 

 ent that substitution by other materials cannot be 

 readily accomplished and means inconvenience, 

 and, in many cases, decrease of comfort. Hence 

 large wood supphes are, and unquestionably will 

 •continue to be, an indispensable requirement of 

 our civilization, almost like water, air, and food. 



Besides wood supplies, the forest furnishes other 

 materials of no small value. Of these, two classes 

 at least give rise to industries of considerable ex- 

 tent, namely the tanning industry and the naval 

 store industry. 



The bark of certain trees, notably the hemlock 

 and the oaks among our native species, contain the 

 chemical compounds known as tannic acids, which 

 serve for the manufacture of leather. The fact 

 that this property of the bark has made the value 

 of the same to exceed by far the value of the wood 

 itself, especially as it is easier to transport the 

 former, has led to an enormous waste of useful 

 wood material, the trees, in mountainous regions 

 especially, having been peeled and left to rot in 

 the woods ; and in certain mountain regions diffi- 

 cult of access this waste still continues. 



Thus 1,500,000 cords of tan bark worth about 

 ^10,000,000, which we use annually, entailed for- 

 merly a sacrifice of nearly 1000 feet of lumber per 



