454 MR. G. ERDTMAN : STUDIES IN THE 
of the bog?" (Jessen, 1920, p. 245). A more detailed account of the 
construction of pollen-diagrams is found on pp. 22-23 (Erdtman, 1921). 
One hundred micro-fossils, amongst others the above-mentioned pollen-grains, 
are figured in * Arkiv for Botanik, Dd. 18 (Erdtman, 1923 a). Docturowsky 
and Kudrajaschow (1923) have published 23 figures of forest-tree pollen. 
2. PEAT MossES INVESTIGATED. 
In modern peat-geolegy with its emphasis upon phyto-physiognomy, 
analyses of the recent vegetation are indispensable for a correct classifieation 
of the different kinds of sedentary (non-transported) and sedimentary 
material, As already mentioned, I had not enough time to make such 
analyses, and thus—even after the microscopic investigations I have made— 
I am unable to give all the deposits met with their descriptive names. 
“ Sphagnum-Scirpus ewspitosus peat," “ Calluna peat," and so forth, are to 
be regarded therefore as provisional names. 
It is a defect in Lewis’s work (“ The Plant Remains in the Scottish Peat 
Mosses ”) that he does not use a fixed terminology. In Part I. he 
distinguishes different kinds of peat, such as Sphagnum peat and Scirpus and 
Sphagnum peat ; later on he also describes layers with Pinus and layers with 
Empetrum ete. In Part IL, alone, he uses the terms “dominant” and 
“secondary " plants, in Part III. “ characteristic ” and “accompanying ” 
plants. Finally, in Part IV. he returns very nearly to the terminology of 
Part I. This manner of description gives us, for instance, very little 
information about the sediments. That there must have been organic 
sediments at some of the places investigated is, however, shown by the 
presence of diatoms and certain macro-fossils, e. g. Potamogeton. The 
occurrence of sediments is also mentioned by Bennie, Reid, and others. 
At this point I take the opportunity of defining, in accordance with 
von Post (1922), some of the organic sediments met with in Scotland. 
1. Clay-Gyttja (Swedish “lergyttja’’).—The name “gyttja” (plur. gyttjas; 
Swed. “gyttjor”) is applied to such sediments as give a green or greenish 
extract when treated with alkali, “ Dy” treated in the same way gives an 
extract where brown is the prevailing colour. 
Clay Gyttja is a dense, somewhat elastic substance, without evident phyto- 
structure, 7, e. structure caused by plant-remains. It has a small content of 
sand or clay. The colour is yellow-grey or blue-grey with a suspicion of 
green. It turns white when dried. The alkaline extract is either greenish 
or colourless. 
2. Plankton-Gyttja.—A dense, usually elastic, sometimes almost rubber- 
like substance, without phyto-structure. The colour is green (almost vivid), 
yellow-green, or brown-green of various shades. On exposure to the air it 
usually darkens rapidly, but, when dried, the bright colour returns. Alkaline 
extract green. 
