146 THE BOG. 



we shall now see that the former, the Mosses, 

 are not less instrumental in the formation of peat- 

 bogs. 



Many years ago the ground on which we are 

 standing was considerably lower than it now is. 

 Instead of being composed of water and mud, it 

 was probably a hollow place, presenting only a 

 rocky surface, or furnished with a scanty coating 

 of mould washed down from the adjoining banks. 

 During the rainy season water would lodge here, 

 forming a shallow pond, on the edges of which 

 germinated the seeds of several species of moss, 

 which delight in excessive moisture.* These 

 gradually extended over the whole area occupied 

 by the water, and rose above its surface, forming 

 a congenial place of growth for many aquatic 

 plants. These mosses are furnished with very 

 long stems, the lower portions of which, having 

 flourished for a definite period, decayed, while 

 the upper parts still continued to vegetate. Their 

 decomposed substance would afford a kind of soil 

 favourable to the growth of other plants, the seeds 

 of which would be lodged here by the wind or 

 floods, till, in the course of a few years, the 

 ground bore on its surface a half-floating mass 

 of vegetation, the moss still elongating itself, and 

 striving to overtop the other plants which grew 

 among its tangled stems. The bark of many of 

 these plants is furnished with a substance which, 

 when dissolved in water, possesses the peculiar 

 property of preserving from decay most kinds of 

 vegetable as well as animal matter. This is the 

 astringent substance called tannin, found so abun- 



* Sphagnum obtusifolium and S. acutifolium. 



