18 GENERAL HISTOBICAL SUMMARY. 



mass which dries into a hard mass with extreme shrinkage, which is then no 

 longer plastic in water. It consists of finely divided plant remains arising 

 from the excrement of water animals, particles of hmnus material, and, for 

 the remainder, of the same materials as muck. The animal excrement, how- 

 ever, is more abundant, the diatoms less. Moor soil is formed chiefly in lakes 

 and ponds in forests, when they contain much humus material in solution 

 which is precipitated by lime salts. Peat consists of brown organic masses of 

 plant remains which have not been eaten. It is deposited in a mass consisting 

 predominantly of animal excrement, and contains diatoms and animal remains 

 in small degree. Peat arises in waters which are more or less clothed with 

 aquatic plants. Besides the common grass-peat, the moss-peat of the conif- 

 erous forests is characteristic for Sweden. In ponds containing Calla and 

 Menyanthes there develops a vegetation of Sphagnum, upon which later 

 Calluna and Ledum, as well as spruces and pines, establish themselves. In 

 more northern regions, lichens overgrow the moss-peat, especially Cladonia 

 rangiferina and Biatora icmadophila. A peculiar kind of peat is carr-peat, 

 which consists of the roots of sedges, CaJxmiagrostis arctica, Deschampsia flexu- 

 osa, etc. Mull or humus consists of digested plant-parts and animal remains, 

 together with brown granular amorphous particles, which are to be regarded 

 as precipitates of humus salts. These are insoluble in water, acid, and alkali. 

 Between these constituents occurs an equal amoimt of animal excrement. 

 The various kinds of humus are moss and lichen humus which consist pre- 

 dominantly of animal remains, coniferous forest humus consisting of decom- 

 posed wood, mycelia, etc. Deciduous forest humus, darker than the fore- 

 going, is rich in excrement and animal remains, and contains much humic acid. 

 Grass-humus consists chiefly of animal excrement mixed with sand and clay. 

 Gremblich, 1876.— Giemh]ich (1876, 1878:1014) called attention to the 

 succession in a particular area of different formations, each of which prepared 

 the way for the following one : 



"We see certain formations invade an area, dominate it for a while, and then 

 disappear, until finally the rotation of formations falls into inactivity, in order 

 perhaps to begin a new cycle which takes the same course. If one follows 

 the course of succession in a moor, he will notice that in general three clearly 

 marked phases may be distinguished. The first phase has for its task the 

 preparation of the bare ground for vegetation. The second is marked by a 

 cover which shows great luxuriance, both of species and individuals. In the 

 last phase, appears a plant covering which closes the rotation of organic life, 

 and marks the death of the succession. The last two stages as a rule store up 

 carbon dioxid in some form, e. g., wood, peat or humus. Each succession in 

 a particular area shows close relationship with that of the moor, and the 

 development of the latter may be taken as the type for all successions. We 

 venture to say that moor succession or some parallel development takes place 

 wherever man leaves natm-e to her own course." 



Gremblich also described the invasion of talus in the Dolomites of the 

 Tyrol, and pointed out the three successive phases of development. The 

 first phase was marked by Hchens and low herbs, Thlaspi, Galium, Saxifraga, 

 etc. The humus thus produced was invaded by Adenostyles, Ranunculus, Saxi- 

 fraga, Rhododendron, Rosa, Rhamnus, Crataegus, Alnus, and Pinu^, as the most 

 important species of the second phase. The last phase was marked by the 



