division, and in some cases noticed certain contradictions. Anyhow 
for the present it is impossible to parallel the Upper Silurian strata 
of Gothland with those of Oesel, a question, indeed, which for a 
determination of boulders of that age can hardly be dispensed with. 
We may sincerely hope that the researches by Horm, who has been 
engaged in this question, may not be long in coming, and that this 
solution may finally settle the question! 
(The chief literature about this controverted question follows here : 
Aes 215 225 27; 28, p- 416; ete). 
Nevertheless in enumerating the species of boulders we must 
adopt a certain succession of strata to arrive at the determination 
of their age. I select for this purpose Scumipt’s division of the 
Eastern Baltic Upper Silurian (8, p. 41—54), corresponding to the 
method hitherto followed in the museum: 
G.1. Jérden Beds. 
2. Borealis bank. 
3s. Ratkull Beds. 
Pentamerus-esthonus zone. 
Lower Oesel zone. 
Upper Oesel zone: 
Lf sNorthern yellow zone: 
2, Southern grey zone. 
Py 
Dames (22), Srorrer (30), SrecertT (32), and others have founded the 
determination of their erratics on the division of Gothland by Linp- 
STROM; as it seems to me, however, that our boulders approach the 
Eastern baltic rocks much more, I did not follow this example, 
the more so, as I have said before, the above-mentioned opinion, 
which is quoted below with the alteration introduced by Damns, 
does not appear to me to be the right one in every respect. 
a. Oldest red shale beds with Arachnophyllum. 
b. Stricklandinia-shale. 
ec. Shale beds and sandstone. 
d. Bands of limestone and shale, in some parts oolite. 
e. Pterygotus-beds. 
Crinoid- and Coral-limestones with intermediate Stromatopora- 
riffs, Gastropoda- and Ascoceras-limestones, together with Mega- 
lomus-banks. 
g. Upper Cephalopodan strata. 
The material may best be subdivided into four groups: I Boulders 
of the age GG; Il... H; Wl... 2; IV... K. The last division 
will appear to be by far the most important. Besides there are some 
35* 
