296 PAST CLIMATES AND CLIMAXES. 



of organic material being stopped as a result of the destruction of the vegeta- 

 tion by flooding or by flooding with deposition. This may happen in the midst 

 of a bed also, and it may occur in the peat-bogs of to-day, as well as in the coal- 

 producing swamps of the past. In either event, the organic matter is mixed 

 with an increasing amount of detritus. The coal passes into carbonaceous 

 shale, and then into pure shale, followed by another bed of coal or by sand- 

 stone, limestone, etc. Vegetation may continue to live and its organic matter 

 to accumulate in a stase, while considerable detritus is being washed into the 

 swamp. From the standpoint of succession, however, the stase may be 

 regarded as closed, and the strate begun at the point where the inorganic 

 material exceeds the organic. Such a point marks a break in the development 

 of vegetation, though the process of deposition may be continuous. It is 

 problematical whether coal may occur in strates formed by the drifting of 

 trunks and other plant material. From the analogy of peat formation, this 

 would appear to be impossible. Beds of coal must have been laid down essen- 

 tially in situ, though it is clear that local drifting must have occuired in the 

 water-bodies of a large swamp. This must have been of Httle significance, 

 however. In the peat-bogs of to-day, the drifting or blowing-in of trunks, 

 twigs, or leaves furnishes evidence of great successional value, but it has only 

 a slight effect upon the amount of organic acciunulation. 



Deposits intermediate between the strate and stase may also arise from the 

 interaction of water and another agent, or from the double r61e of water as 

 an agency of transport as well as of accumulation. Examples of the latter 

 occur especially in calcareous tufas, and perhaps also in breccias and sinters. 

 In the former, at least, the tufa or travertine may envelop plants in situ, or 

 transported parts, or it may inclose both, as seems usually to be the case. It 

 may be either stase or strate, or a combination of the two in varying degree, 

 though the strate usually predominates. In such deposits it is clear that the 

 wind or some other agent may act as the agent of transport in the place of 

 water. The calcareous deposits of caverns may also bury and preserve the 

 remains of plants and animals, as already noted. In such cases, man is 

 usually the agent of transport, and the deposit is essentially a strate, though 

 the completeness of the sequence often gives it something of the value of a 

 stase. This is notably the case in the Cave of Castillo near Puente Viesgo, 

 in northern Spain, where 12 successive strata have been discovered, repre- 

 senting the Acheulean, Mousterian, Aurignacian, Solutrean, Magdalenian, and 

 Azilian cultures (Osboru, 1915: 164). Finally, an interesting mixtiu-e of stase 

 and strate arises when a stase is eroded and the material deposited again, 

 either in a strate or in connection with another stase. This is a regular 

 occurrence in the denudation of peat-bogs. 



Belation to stratigraphic units. — ^While the terms employed in stratigraphy 

 vary both in concept and usage, their general usage is suflSciently uniform to 

 permit comparison with the various kinds of strates and stases. The con- 

 cepts adopted here are those of Chamberlin and Salisbury (1906:1:487). 

 Bed and layer are regarded as synonyms, with lamina as a subdivision. For- 

 mation is the term appKed to all the consecutive layers of the same rock, while 

 stratum may be appHed to one or several layers, or used in the plural in a gen- 

 eral sense, comparable to the use of community in vegetation. All the forma- 

 tions of a period form a system, which may consist of two or more series when 



