280 Twenhofel — Notes on Black Shale in the Making. 



slime. But if this should occur, the heavier bowlders would 

 be very apt to siuk in the slime for one or two feet, while the 

 smaller oues would remain suspended above. 



How thick these slimes are, and what is probably of greater 

 importance, how thick they may become, is not known. In 

 the Lyckholm and Arensburg bays, it appears fairly probable 

 that they may be fully a score or more feet thick and, if slow 

 depression has occurred, there is the probability of an exten- 

 sive thickness. Further, there should be an extension sea- 

 ward as the lightness of the slimes readily permits transporta- 

 tion. And it appears that this actually takes place at Hapsal, 

 judging from the strong odor of slime which exists near the 

 water. In respect to area involved it is difficult to give definite 

 quantitative data. Estimations made from Lange's map give 

 the areas of the four localities described above, as having 

 between pei'haps 150 and 200 square km. over which the 

 slime occurs, with probably from 75 to 100 square km. having 

 it as a deposit of considerable thickness. 



The origin of the slimes is probably related as a first cause 

 to the tranquility of the water in the bays and sounds, since 

 similar deposits are not forming in the open places. Secondly, 

 it is probable that the absence of tides and the character of the 

 climate permits the vegetation to flourish in the manner de- 

 scribed. Conditions of a similar character may have obtained 

 in the development of the Paleozoic black shales, but on that 

 point nothing can be said. 



There appears to be little doubt that these deposits on com- 

 pression would form black shales and would have most of the 

 characters typical of such. They would carry a fauna of 

 species with small thin shells and these would probably be 

 largely preserved as pyrite or marcasite replacements. They 

 would probably also occur in great abundance at various levels 

 from being carried in by storms, but be generally rare. It is 

 possible that thin conglomerates would be present ; but, if so, 

 it is probable that the coarser bowlders would be below, while 

 above there would be a gradation to finer shales. The shale 

 bands would have no flanking clastic deposits, except locally, 

 and would be long in respect to width, approaching, however, 

 in no way the great lengths of some of the Paleozoic black 

 shales. Furthermore, their extensive distribution in local 

 basins might lead to an inference of continuity of the separate 

 areas, especially if the intervening deposits were covered. 



As a conclusion, the writer considers it absolutely certain 

 that black hydrocarbonaceous shale may form in water so shal- 

 low that it is but a step to land conditions, and that their pres- 

 ence is by no means an evidence of deep water. 



University of Kansas, Lawrence, Kansas 



