] 
; 
Proceedings. 21 
This gives 13 genera and 61 species peculiar to the Tremadoc 
Slates. As I stated earlier on, the Geological Survey class the 
Tremadoc Slates with the Cambrian, but the Continental geolo- 
gists place them with the Ordovician. From the figures I 
have just given, and the fact that such important families as 
the Lamellibranchs, Graptolites, and Cephalopods appear first 
at this stage, the evidence seems to me to support the foreign 
classification. 
A careful zonal examination of the strata may, however, 
possibly show that errors have been made by collectors, and 
that the fauna is not so mixed as at present appears to be the 
case. Thus some of the beds containing primitive forms may 
be relegated to the Lingula Flags, while those with a larger 
_ proportion of later forms may fall into their place, at the base 
of the Ordovician. 
We will now consider for a few moments the relative age of 
the deposits in N. and 8. Wales, and in Shropshire. 
The zone of the graptolite Dictyograptus socialis has been 
taken as the upper limit of the Lingula Flags or the base of the 
Tremadoc. We find this zone in N. Wales and also in Shrop- 
shire and at Malvern; thus some portion at any rate of the 
oldest beds are found in these two districts. The fauna of 
the Shineton Shales, with its various Olenide, alone is suffi- 
cient to suggest, apart from the Dictyograptus, that this was 
the case in Shropshire. At Carmarthen this graptolite zone 
has not been found, but lithologically the beds are very similar 
indeed to those at Shineton: and the presence of Hrinnys, a 
Lingula-Flag form, together with two or three genera of the 
Olenidz, strengthen the opinion that these beds are probably 
of about the same horizon as the Shineton Shales. 
In attempting to arrange chronologically these deposits, our 
great difficulty is that few fossils are common even to two 
areas. N.and S. Wales have only two trilobites (out of a total 
of 11) in common—Wiobe Homfrayi and Asaphellus Homfrayz ; 
and only one in common with Shineton, Asaphellus Homfray ; 
and not one with Carmarthen. Not one Olenid is found at 
St. David’s. 
