Twenhofel — Notes on Black Shale in the Making. 279 



parts of the north and west coasts of Oesel. The deposits have 

 also been considered by Eichwald,* Schrenck f and Goebel4 



In Baltische Landeskunde the slime is described as having a 

 more or less dark color and being broth-like to jelly-like when 

 wet. When dried it becomes a firm mass which is able to be 

 cut and affords a valuable fertilizer. Anaerobic bacteria appear 

 to have taken a large part in its development. The microscope 

 shows that it contains very small pieces of plant tissue and 

 excretions and the sheddings of animals.§ 



The macroscopically visible fauna of these deposits is not 

 large and the shells are small. They belong to species which 

 are normally of considerable size ; but which, under the brackish 

 water conditions of this part of the Baltic, attain dimensions 

 but little more than a fifth or a fourth so large as the norm. 

 Few examples were seen directly in the shales and they were 

 seen in close contiguity only along the shores of the sound 

 between Moon and Oesel. Four species were collected at this 

 locality. They are Limnea ovata oaltica, Mytilus edulus, 

 My a arenaria and Gardium edula ; not one of which is over 

 one half an inch long. The shells of each species are very 

 light and float easily and in many instances they were seen on 

 the beach in great numbers. They had been thrown there 

 by high waves, and there is no doubt that they are frequently 

 so introduced in equally great numbers into the slimes. 



The strong sulphur content of the slimes should certainly 

 precipitate any iron therein contained as pyrite or marcasite, 

 and this would almost certainly replace the calcite or the 

 shells. The extreme fineness of the muds and the fact that 

 the upper layers are rather fluids than solids are conditions 

 which readily lend themselves to the development of hydro- 

 carbons of various kinds, thus giving rise to a shale rich in 

 these substances. 



Another feature of the slime deposits that is of some im- 

 portance is that they are not generally flanked by littoral or 

 shore deposits. This results from the fact that the vegetation 

 covers the shore to below the water level, thus protecting it 

 from wear and not permitting the segregation of clastic 

 deposits. Hence, if these slimes should fortunately be pre- 

 served, they would not be flanked by any clastic deposits as 

 postulated by Ruedemann, except perhaps locally. Also a 

 violent storm might suffice to carry gravel from a local deposit, 

 or from the mouth of the bay or sound and mingle it with the 



* Eichwald, Bull, de Moscou, i, p. 414, 1852. 



f Schrenck, Uebersicht des obersilurischen Schichtensy stems Liv- und Ehst- 

 lands, etc., Lorpat, 1852, p. 102. 



JGoebel, Archiv fur Naturkunde Liv-,Ehst- tmd Kurlands, 1852, ser. (1), 

 i, p. 113. 



55 E. V. Wahl and K. H Kupfer, Baltische Landeskunde, Eiga 1911, p. 

 242. 



