W. G. Fearnsides—Lower Ordovician Rocks of Scandinavia. 267 
ages, and that the first one being buried in sediment the superposition 
of the second over a part of the site of the first must be accidental. 
As now obseryed the neighbouring pits occur so close together that 
over a district which, despite the ravages of denudation, still measures 
some 500 miles from north to south and 250 from east to west, it is 
rare to find a horizontal distance of more than a few inches without its 
pit. That at any imstance during their formation the pits were so 
close as this is not, however, clear, and, when one considers the vast 
thicknesses of correspondingly coarse material which were accumulated 
during the period of the Glauconiteskiffer and Ceratopygekalk, is not 
probable. The infilling matter of the pits is almost always glauconite- 
bearing, and whether the matrix be soft shale or hard limestone it is 
noticeable that larger glauconite grains and rolled fossil fragments line 
the bottom, while smaller glauconite grains and matrix fill up the rest 
of the hollow. In this description I have hitherto only mentioned the 
Erosion pockets or Korrosionsgruppar, which occur at the surface of 
separation between the glauconite group and Alum Shales below. 
There the phenomenon is undoubtedly most easy to follow, but. 
throughout the Glauconite shale and Ceratopygekalk each and every 
bedding plane which carries glauconites shows also Erosion pockets. 
The Orthoceras limestone also, where glauconitic, continues the same 
phenomenon on a more limited scale, “and even where not glauconitic 
certain of its beds*show a Korrosionsgruppar (or pocket erosion ) 
arrangement of the coarser fragments in holes bored into more 
homogeneous material. Within the Ceratopygekalk bedding planes 
with Korrosionsgruppar occur so abundantly and near together that 
the successive lamin interlock very intimately, and a considerable 
thickness of this slowly formed rock is rendered quite thick-bedded 
and massive in appearance. A freshly broken block from such a rock 
has the aspect of a photograph of a gravel-pit where the gravel, once 
calcareous, has suffered loss by solution, and has sagged down into 
the pipes so common under those circumstances. 
EXPLANATION OF PLATHS.! 
Puare VIII.—Generalized section along the west coast of the Island of Oland, 
showing the actual succession and mutual relationships of the various sub- 
divisions of the Cambrian and Tremadoc rocks there exposed. Actual observation 
points are indicated by solid lines. 
Prare [X.—Erosion pockets or ‘ Korrosionsgruppar’ at the base of the Tremadoe 
Series of Vestergétland. 
Fig. 1. Northern face of a block showing the irregular boundary between 
calcareous glauconitic shale with Orthis Chr istiani, Euloma, Niobe, etc., and an 
even-bedded orsten of the Peltwra scarabeoides zone. 
Fig. 2. Western face of the same block showing similar phenomena. Note 
here the sharp cusp at the northern (right-hand) end of boundary-line due to the 
intersection of erosion pockets of different ages. 
Fig. 3. Under-surtace of same block showing good heads, etc., of Peltwa 
scarabevides undisturbed by the processes of erosion which have produced the 
adjoining Korrosionsgruppar. 
The block, three surfaces of which are here depicted natural size, was collected at 
Ulunda Stenbrot, about one mile east of the church of Varnhems Kloster, Vester- 
gotland. 
1 Plate X will appear with the conclusion of this paper in the July Number. 
(To be coneluded in our next number.) 
