188 bulletin: museum of comparative zoology. 



At Packerort the most fossiliferous layers are in the upper part of 

 the shale, and it might be inferred from this that in the eastern region 

 the upper layers had been removed by erosion, but it is equally possible 

 that they were never deposited there. 



The characteristic fossils of the Packerort formation are the various 

 species of Obolus, chiefly 0. apolUnis, in the sandstone, and Didyoncma 

 flaheUiformc in the shale. Species of other genera of inarticulate 

 brachiopods- are found in the sandstone, and the shale has furnished 

 several species of graptolites which have not yet been satisfactorily 

 identified. If Schmidt's (44, p. 16) figures are to be trusted there may 

 be a Didymograptus in this fauna. 



The Obolus or Unguliten sandstone, has, like the Lower Cambrian 

 clay of the same region, often been cited as an example of a formation 

 which has never been consolidated. At nearly all exposures it is a 

 friable sandstone which crumbles readily under the hammer, but in 

 certain places it has considerable hardness, and one receives the 

 impression that the present condition is due to the removal of the 

 cement through leaching. The surface water enters the sandstone 

 through joints in the overlying limestone, and being checked in its 

 further downward passage by the Cambrian clays, naturally moves 

 through the sandy beds. 



Walchow formation. B, and B,i (Glauconitsand and the Glauconit- 

 kalk) of Schmidt; Bj, Bii„, B,,^, Bi,^ and Bmo, of Lamansky. 



While the Packerort formation is best developed at the extreme 

 western end of the Ordovician outcrop, the succeeding formation finds 

 its best expression in the east. This, however, is not due to the fact 

 that the Walchow formation was deposited in a sea invading from the 

 east, for the opposite seems to be the case, but because the upper 

 layers have been eroded away at the west, as has already been shown 

 by Lamansky (29). The lower members of the formation, the " Glau- 

 conitsand" and the " Glauconitkalk" are better developed in the west 

 than in the east, and the deposits of the same age as the Glauconitkalk 

 are still thicker in Sweden. 



On the W^alchow and on the Lawa at Wassilkowa this formation 

 has five bands easily distinguished on lithological grounds, each with 

 its own faunal characteristics. The measurements given here are 

 those of the section on the Lawa which presents a more satisfactory 

 natural section than any seen on the Walchow. (Plate 4). 



The lowest bed is a soft, easily disintegrated green sandstone, six 

 feet in thickness. Upon it rests two or three layers of limestone, 

 making a total thickness of six feet, which usuklly form a bold pro- 

 jection from the cliff, being preceded and followed by softer strata. 



