70 
HUGHES : INGLEBOROUGH. 
could establish its occurrence here. The Ceratiocaris described 
by Dr. Woodward, ib., p. 205, should also be found at the same 
horizon. 
Cardiola Interrupta Brod. 
This species is, I believe, so far as at present known, absolutely 
confined to the Silurian rocks, and therefore most useful when 
we are trying to separate them from the Bala Beds which they 
often much resemble in lithological character. 
I have hammered out Cardiola interrupta in the Sedbergh 
district, in Hebblethwaite Gill for instance within a few inches 
of the base ; I have found it also in the highest beds of the 
Ludlow Rocks, and it occurs here and there throughout the 
intermediate beds. 
Barrande states that it occurs in the Bala Series, but that 
is due to a mistaken identification ot strata. When I commenced 
to map the Silurian rocks of the north of England the Coniston 
Grit was called Caradoc Sandstone, and as Cardiola interrupta 
was the most marked fossil of the Coniston Grit, it got into 
Etheridge's list of Caradoc fossils. On that authority Barrande 
put it down as a Caradoc form. As the result of my mapping 
and fossil collecting I inferred that the Coniston Grits and Flags, 
in fact, everything down to the Austwick Conglomerate, was 
Silurian, i.e.. Upper Silurian of the Survey, so that there was, 
as yet, no authority for putting Cardiola interrupta into the 
list of Caradoc or Bala fossils.* Owing to circumstances over 
which I had no control I was not then able to foUoAv the matter up. 
It may be useful here to call attention to the progress of 
identification and subdivision of the Silurian rocks of this district 
and the changes and limitations of nomenclature which 
accompanied them. 
Before the six -inch ordnance map was published, and in 
some cases before there was even a one-inch map to be obtained, 
it was difficult to fix and trace boundaries, estimate thicknesses, 
and define exactly the groups of strata referred to. It may 
be that these and other difficulties in the way of working out 
* Geol. Mag., vol. iv., No. 8, Aug., 1867, p. 11. 
