68 Dr. J. EF. Marr—The Ashgillian Series. 
In Scandinavia we find records of fossils from the Brachiopod-schists 
in Linnarsson’s account of the Cambrian and Silurian Beds of Westro- 
gothia (K. Svensk. Vetensk.-Akad. Forhandl., Bd. viii, No. 2; in this 
paper some of the forms are apparently from the Upper Brachiopod 
schists, of Llandovery age) ; and also in Tullberg’s papers on the Scanian 
graptolites (Svensk. Geol. Undersdékn, series C, No. 50, p. 17), in the 
zones of Stuurocephalus clavifrons and Phacops mucronata. Records 
of fossils of the Zeptena Limestone will be found in various papers by 
Tornquist, especially in a paper on the Paleozoic rocks of the Siljan 
district (Ofvers. af k. Vetensk.-Akad. Forhandl., 1874); and another 
on the trilobite fauna of the Siljan district (Sver. Geol. Undersokn, 
1884); also in Angelin’s ‘“ Paleontologia Scandinavica”? and in 
Lindstroém’s ‘‘ Fragmenta Silurica.” 
A list of Russian fossils from Stage F will be found in the first 
part of Schmidt’s ‘‘ Revision der Ostbaltischen Silurischen Trilobiten ”’ 
(Mem. l Acad. Imp. des Sciences de St. Pétersbourg, 1881). 
The above list is no doubt far from complete, but the student may 
obtain from a perusal of these papers a good idea of the varied 
character of the Ashgillian fauna. 
IV. Tue Base anv Summit oF THE ASHGILLIAN SERIES, 
(1) Base. In South Wales, where the Ashgillian succession is so 
well shown, the line of demarcation between the Robeston Wathen 
Limestone of Caradocian age and the Ashgillian Sholeshook Limestone 
is usually easily determinable. Although each is a limestone, they 
are fairly readily separable by lithological characters, and the change 
in fauna is very marked. Similarly, in the Lake District the change 
from the Caradocian Sleddale Limestone and the Ashgillian Stawro- 
cephalus Limestone is usually well marked, though it is possible that in 
the fossil lists some forms referred to the Caradocian division really 
belong to that of the Ashgillian. In the Cross Fell Inlier the 
difference between the equivalent of the Sleddale Group (Dufton 
Shales) and the Ashgillian Limestones is most obvious. The exact 
base of the Ashgillian group at Girvan yet remains to be fixed, and, 
as before stated, much remains to be done in North Wales. 
(2) Summit. The line of demarcation between the Ashgillian and 
Valentian is usually less readily determinable than that at the base 
of the former series. The difficulty was admitted by Salter when he 
bracketed the Lower Llandovery and Upper Bala Groups (Cat. Camb. 
and Sil. Foss.). 
There are two causes of difficulty; one the frequent similarity 
between the Ashgillian and Llandovery rocks, and the other the 
difference of opinion as to what line should be taken as marking the 
top of the Ashgillian. With regard to the former, the Ashgillian and 
Llandovery Beds of the Haverfordwest region have a striking similarity, 
though separated by a conglomerate, and in Scandinavia the line of 
demarcation must be drawn in the middle of the Brachiopod-schists. 
I believe that the fossils will usually furnish a ready means of 
distinction. The practical disappearance of Zrinucleus at the top of 
the Ashgillian has already been noted, and, so far as I know, the 
genera Widulites, Phacops (proper), and Stricklandinia are not found 
below the Lower Llandovery. 
