12 GENERAL HISTORICAL SUMMARY. 



De Luc also noted the significance of wet and dry periods in the develop- 

 ment of the bog: 



"The surface of these pits is covered with all kinds of ligneous and aquatic 

 plants that deUght in such a soil; these alternately overtop each other; the 

 ligneous plants make the greatest progress in a dry summer, so that the surface 

 seems to be entirely covered with them . The reverse is the case in a rainy 

 suromer. The aquatic plants overtop the ligneous and choke them insomuch 

 that the whole surface seems to be entirely covered with a matting of aquatics 

 which, by decaying, form a soil for the ensuing season. If it continues rainy 

 for a succession of years, these aquatic plants continue to prevail till a dry 

 season comes. This is so certain, that in the succession of beds, or strata of 

 the moss, these different species of plants are distinguishable. These strata 

 are either composed of the roots and fibres of ligneous plants, or of the remains 

 of aquatic; so that upon examining some of the cuts of the deepest canals, 

 one saw distinctly the produce of the several years, and could even distinguish 

 the different produce of a wet and dry season, from the residuum each had left." 



Rennie, 1810. — Rennie, in his "Essays on the Natural History and Origin 

 of Peat Moss," gave the first comprehensive and detailed accoimt of peat- 

 bogs. His book is an almost inexhaustible mine of opinions and observations 

 from the widest range of sources. It must be read in detail by everyone who 

 wishes to be familiar with the beginnings in this most important part of the 

 field of succession. The titles of the nine essays are as follows: 



I. Of Ligneous Plants. 

 II. Of Aquatic Plants. 



III. On the Changes and Combinations by which Vegetable Matter is converted 



into Moss. 



IV. On the Simple and Compound Substances that may be Expected and are 



ReaUy Foimd in Peat Moss. 

 V. On the Alliance Between Peat, Surtur-brandt, Coal, and Jet, 

 VI. On the Alliance between Peat and Other Bituminous Substances. 

 VII. On the Distinguishing Qualities of Peat Moss. 

 VIII. On the Sterility of Moss in its Natural State, and Causes of it. 

 IX. On the Different Kinds and Classification of Peat Moss. 



Rennie discussed at length the relation of forest to peat-bogs, and stated 

 that in many bogs one tier of roots appears perpendicularly above another, 

 while in some even three tiers appear in succession. Trees are also found 

 growing upon the ruins of others after they have been converted into moss. 

 He cited the observations of the Earl of Cromarty with reference to the 

 replacement of forest by bog: 



"That, in the year 1651, when he was yet young, he visited the parish of 

 Lochbroom in West Ross; that he there saw a small plain covered with a stand- 

 ing wood of fir trees, which were then so old that they had dropped both 

 leaves and bark. On a visit to this forest 15 years afterwards, not a tree was 

 to be seen, and the whole plain was covered with green moss. By the year 

 1699, the whole had been converted into a peat moss from which the inhabi- 

 tants dug peat." 



The author quoted many opinions upon the secondary development of peat 

 when the original deposit had been dug, and concluded that the conditions 

 requisite for regeneration were that the pits be full of water, and that the 

 water be stagnant. The process went on most rapidly in small pits with 



