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to pay a visit to Scania and Oesel; the material for comparison 
from those regions (present in the Min.-Geol. Institution in this 
town, for the greater part collected by Mr. J. H. Bonnema), however, 
will make up for it to a large extent, though not all questions can 
be solved. 
Some days’ stay at Upsala enabled me, thanks to the kindly 
assistance of Dr. C. Wiman, to examine the collections present in 
the Geological Institution from the different Lower Silurian regions 
of Sweden. This examination, which of course had to be made in 
haste, obliges me to introduce some alterations into my former 
description which however are not very important. By this time the 
material has been increased by new finds, and as more recent 
publications always make some alterations or completions necessary, 
I have made up my mind not to introduce them now but to collect 
all these corrigenda and addenda in an appendix at the end of the 
treatise of the Groningen erratics. 
The real description of the Upper Silurian species of boulders of 
which two have been dealt with in this communication, is preceded 
by some pages which, from an_ historical point of view, are not 
unimportant. After the appearance of my first contribution Dr. L. 
Hormsrröm at Akarp was so kind as to draw my attention to some 
parts of his lately published biography of Orro Torerr. From this 
I learned that, in 1866, the latter had written a prize-essay on a 
subject suggested by the Dutch Society of Sciences at Harlem, and 
treating of the origin of the stones and fossils of the Groningen 
Hondsrug. His essay was rewarded, but was never published and 
not given up to the Dutch Society till after the author's death. 
Thanks to the kindness of its secretary, Prof. dr. J. Bosscna, I have 
been able to study TorerL's essay, and now comprehend his relation 
to the Groningen boulders which formerly really puzzled me. His 
ideas about our subject are a necessary completion of the historical 
outline. 
Finally, it pleases me to state that this year as well as last year 
the support of the Groningen University Fund fell to my share, 
while the expenses of my investigations in Sweden have for the 
greater part been defrayed by a subsidy granted to me by the 
“Central Bureau for the promotion of the knowledge of the province 
of Groningen” after receiving the approval of “the Board of the 
Physical Society at Groningen.” This obvious interest taken in the 
subject of my study has been a source of much delight to me. 
