Geology. — ‘Some new sedimentary boulders collected at Groningen’. 
By Dr. P. Kruizinea. (Communicated by Prof. G. A. F. 
MOLENGRAAFF). 
(Communicated in the meeting of May 31, 1919.) 
Some ten years ago a favourable opportunity offered for collecting 
sedimentary boulders at Groningen, where in three different spots 
at the northern extremity of the Hondsrug and in the neighbourhood 
of the northern cemetery, which has already become known as a 
findingplace of erratics, important excavations were performed. First 
when the foundation was laid for the new tram-shed, and shortly 
after when new streets were being made, viz. the Tuinbouwstraat 
and the Koolstraat. 
When trenches were dug for sewer-pipes, the Dilivium was not 
reached at the point, where the Tuinbouwstraat joins on to the 
Nieuwe Ebbingestraat. The presence of sherds of pottery at a depth 
of more than 1 m., however, made us suspect that the upper soil 
had been turned over or earthed-up. A little higher up in the Tuin- 
bouwstraat the Dilivium emerged, and gradually rose to the surface, 
until about halfway it was seen half a meter above the present 
level of the street and was covered only by a thin layer of mould. 
Subsequently it first sank again below the street-level, after which 
it rose once more to the height just mentioned. Afterwards, on the 
occasion of the excursion made in 1913 by the Geol. Section of the 
Geol. Mijnbouwkundig Genootschap (28 p. 83), it was encountered 
again in the first part of the Verlengde Tuinbouwstraat, also covered 
with a layer of mould. 
In the three localities just mentioned boulder-clay was found, 
which is calcareous but already oxidized. Besides this a number of 
bands of gravel were to be observed. 
Among the large number of boulders, found by me during these 
excavations, there were several interesting specimens. Of the species 
rarely found near Groningen I mentioned already (30 p. 231) the 
Upper-Silurian limestone with Pristiograptus frequens Jaek. and the 
Saltholms-limestone (also the glauconitic variety, the so-called Glau- 
conitie Terebratula-rock) from the Danian. 
In the following pages I purpose to discuss three more Silurian 
