Dr. J. E. Marv—The Ashgillian Series. 63 
The distinctness of the Caradocian and Ashgillian Series, over wide 
areas, as based upon lithological characters and faunas, was thus for 
the first time clearly brought out, and a fairly definite base and 
summit for the series which I here speak of as Ashgillian was 
determined. ‘The Ashgillian Series was, in fact, here clearly deseribed 
as 2 group worthy of separation from the Caradocian series beneath. 
Our classification of these South Welsh deposits has subsequently 
been confirmed by the officers of the Geological Survey, and later by 
Mr. D. C. Evans im an admirable paper on the Ordovician of Western 
Caermarthenshire.* 
Let us return for a moment to North Wales. The fossils of the 
Rhiwlas Limestone undoubtedly show its relationship to the Sholeshook 
and Staurocephalus Limestones, and prove its distinction from the 
Bala Limestone of Caradocian age. This distinction, as I stated in 
my Presidential Address in 1905, was clearly suspected by a member 
of the Geological Survey in 1847. 
In that address I divided the Ashgillan Beds of North Wales as 
follows :-— 
Hirnant Limestone. 
Shales. 
Rhiwlas Limestone. 
There is still much work to be done among these North Welsh 
rocks. In 1880? I referred a calcareous grit with Lchinospherites, 
‘by the roadside about a quarter of a mile south-west of Maeshir,” 
to the ‘‘ Upper Bala Beds.”’ This is probably correct, but a further 
reference of the Orthis alternata beds of Cerrig-y-druidron to this 
series is almost certainly an error. 
When the Ashgillian Beds of this region are eventually defined 
the definition will undoubtedly be facilitated im consequence of 
Mr. T. Ruddy’s paper on the area. It is quite clear that some of 
the rocks described by Mr. Ruddy belong to the Ashgillian division. 
Miss Wood (Mrs. Shakespear) and Miss Elles have obtained undoubted 
Ashgill Shales with Phacops mucronatus near Conway (QJ.G.S., 
vol. lu, p. 273). 
As in the case of South Wales, so here, we are in difficulty as to the 
precise position of the upper limit of the Ashgillian strata. 
In 1882+ Professor Lapworth described the Girvan succession in 
Ayrshire. At the top of the Ordovician system he places the 
Drummuck Mudstones, with the following subdivisions :— 
Upper Mudstones, Ladyburn. 
Starfish Band, Quarrel Hill. 
Lower Mudstones, Drummuck. 
Basal Sandstones, Auld Thorns. 
In our paper on Haverfordwest Mr. Roberts and I remarked that 
“the Starfish Bed of Professor Lapworth . . . . may possibly 
be the representative of this [Sholeshook Limestone | in the Girvan 
area. It also contains Stawrocephalus globiceps.’”” There is very little 
Q-J.G: S , vol. xii (1906), p- 597. 
2 Q.J.G.S., vol. xxgevi (1880), Dp: 277- 
3 QI.G , vol. xxxv (1879), p. 200. 
= Q.J.G a , Vol. xxxvili (1882), p. 537. 
