138 HIND : CARBONIFEROUS ROCKS OF ISLE OF MAN. ' 
Gumming showed as long ago as 1848 that the Carboniferous 
Series in the neighbourhood of Castletown could be divided 
into four sub-divisions : — 
The Posidonian schist = Posidonomya Becheri beds, 
Poolvash Limestones. 
The Lower or Castletown Limestones. 
Basement conglomerate. 
But the series is not as simple as this classification would suppose. 
While the basement conglomerate is undoubtedly over- 
laid by well-bedded limestones at Derbyhaven, Langness, and 
Port St. Mary, the relation of the so-called Lower Limestones 
to the Poolvash series of richly fossiliferous, obscurely bedded, 
dome shaped, white, limestones is nowhere seen, but the latter 
are apparently overlaid by the Posidonomya beds. 
The so-called Lower Limestones are to be seen at Derby- 
haven and Ronaldsway, Langness, Castletown, Scarlet, Strand- 
hall, Port St. Mary, and Ballasalla. 
At Scarlet these beds pass up into Black Limestones and 
shales with a fauna which shows them to equal a part of the 
Posidonomya beds. So that without evidence of unconformity 
the Scarlet Limestones and the Poolvash Limestones are over- 
laid by beds of the Posidonomya series. Unfortunately, from 
one point of view, the ground between Scarlet and Poolvash 
is occupied by a series of volcanic ashes and lavas which 
renders further stratigraphical evidence impossible, and the 
present paper is an attempt to settle the question by an 
appeal to palaeontology. 
The question whether the Derbyhaven-Ronaldsway series 
represents a series much older than that of Scarlet, has been 
much on my mind, for there being a gap in the series between 
Langness and Castletown, there is no stratigraphical reason 
why the beds at Langness and Castletown might not be the 
Lower and Upper members of a fairly extensive series and agree 
with the sequence of Arnside, West Yorkshire and West- 
morland, which have beds with Michelinia megastoma at the base, 
with a fauna which points to a Seminula and Upper Caninia 
horizon. 
