Twenhofel — Notes on Black Shale in the Making. 277 



sewed as fossils. In the lower Paleozoic black shales, these 

 are almost invariably present; though not uniformly dis- 

 tributed, but localized in bands. Species of the littoral or true 

 benthonic forms are comparatively rare. The brachiopods 

 belong almost wholly to species having thin phosphatic shells 

 and these are generally of the non-hinged type. Cephalopods 

 occur rarely, pelecypods are not uncommon locally and always 

 with thin shells, gastropods appear to be quite rare, and trilo- 

 bites to the time of their extinction occur quite commonly. 

 Heavy shells of any kind are rare. 



In the writer's judgment there are two kinds of black shale. 

 One of these is the type so common in the Coal-measures of 

 Kansas and elsewhere. In this kind of black shale, the color 

 appears to a considerable extent to be due to contained carbon 

 not combined with hydrogen. The other type is that rich in 

 hydrocarbon. This variety is well exam pled by the Utica as 

 exposed about Ottawa, Canada. And, in any discussion of 

 origin of black shales, the writer believes the two types should 

 be carefully differentiated, as the former is generally of non- 

 marine origin, while the latter is in most cases probably marine. 



Black Shale in the Making. 



In the province of Esthonia, Russia, there are a number of 

 localities along the shores of the Baltic in which deposits of 

 black shale are now forming. Opposite the city of Hapsal is 

 the long peninsula of Nucko, at one time an island. Schmidt's 

 map,* published in 1858, so pictures it and he specifically 

 designates it as such ; but Lange's map of 1914 shows a low 

 connection with the mainland at the north end. The water 

 between the peninsula and the mainland is brackish ; not to a 

 high degree, but similar to that in the Baltic of all this region, 

 although it is sweeter in the bays than outside. At present 

 the bay has a length of about 12 km. and a width at the places 

 to be described of from about 2 to 4 km. Formerly the 

 passage was 15 km. long. Where the Avidths above given 

 obtain, the bay is bordered on one or both sides for a mile or 

 more by swamp land, some of which lies a foot or two above 

 water-level, but of which fully half lies below this level. 

 There is little doubt that these areas were once a part of the 

 bay and have been filled up in the manner to be described. 

 Much of this swamp land has a heavy growth of coarse grasses 

 and reeds, the latter said to be extensively used by the peasants 

 for thatching roofs. In seeking for a place to cross the bay, 

 it was necessary to somewhat extensively explore the swamp 

 and it was found that the substratum is composed of a very 



* Schmidt : TTntersuchnngen uber die Silurische Formation von Eastland, 

 Nord-Livland nnd Oesel, Arehiv fur die Naturkunde Liv-Ehst-und Kurlands, 

 (1), xi, 132, 1858. 



