230 
the first may agree pretty well with SroLLev’s boulders, but neither 
of them agree with the Groningen specimen, especially as regards 
the amount of quartzgrains. 
The presence of erratic blocks with Strophomena Jentzschi Gag. 
in Oeland, Gotland and Gotska Sandön leads us to consider also 
the localities of the Baltic west and north of the last two islands. 
It is true, the erratics found there, differ largely from the Groningen 
boulder; still this district is presumably to be considered as their 
original site. SrouLey and ANDerssoON do the same for their blocks, 
while the assumption also seems warrantable of the presence of 
similar erratics in East-Prussia, notably the one described by Pomprcks 
and the Spittelhof fragment recorded by GAGer. 
Probably this specimen must be considered to originate from a 
narrow slip of the Baltie, a little north of Gotska Sandön and at 
a short distance West of Gotland. 
From the foregoing it appears therefore, that the place of origin 
cannot be assigned more accurately, so that we cannot say for sure 
to which division of the zone Aj,; the boulder belongs. It is 
therefore, like the Strophomena-Jentzschi conglomerate to be classed 
provisionally under By). 
jalcareous Sandstone with Asaphus raniceps Dalm. 
In the Tuinbouwstraat one boulder was found among the many 
erraties that, judging from the fossils it contains, must be included 
among the Lower-Silurian. It is however of a peculiar petrographical 
character, as it consists of rather hard, fine-grained sandstone with 
a caleareous cement. The like of it appeared to be quite unknown 
in the literature of erratics. 
This erratic block has about the size of a child’s head and its 
primitive colour was gray to bluish-gray, as may still be observed 
from the inner part; the outside, however, shows a discolouration 
to brownish-yellow. For the rest it has suffered little from weathering. 
The quartz-grains are small, all but colourless and rounded. | did 
not encounter glauconite, but only some grains of calcite. The rock 
also contains a few pieces of more or less rounded, coarse-grained 
limestone, black at the periphery, white in the centre. These frag- 
ments, which moreover contain a large number of brown, rod-shaped 
bodies, are presumably little rolled boulders since they differ so 
much from the surrounding roek. However this is still highly 
problematical. 
Beyond one specimen of an Orthis-species this block contains a 
