58 J. j R. Balnjns — A Question for Silurian Geologist-s. 
two, as well as tlie smootk extremity of tke shields, have beeil broken 
ofl. Tbe impression of tbe external surface, seen on tbe matrix, 
shows tbat tbe axis of the tboracic segments was marked witb 
scattered tubercles. Tbe cepbalic sbield and pygidium appear to 
bave been minutely granulate. On a portion of the latter tbese 
granulätions bave a scaly form, as in some otber species of tbe genus. 
Tbe ends of tbe pleurse are broad and rounded. (See Fig. 2 a.) 
Tbe borizon of the fossil is the upper part of tbe Arisaig series of 
Nova Scotia, equivalent to the Lower Helderberg of New York and 
Pennsylvania, and to the Ludlow of England. Tbe matrix of tbe 
specimen contained Chonetes Nova-Scotica, Hall ; Älegambonia can- 
cellata, Hall; Avicula Honeymani, Hall; Beyrichia pustulosa, Hall; 
and other fossils cbaracteristic of tbat horizon. 
Tliis fine species is evidently a close ally of H. Knightii of the 
English Ludlow, tkougk it differs considerably in details of structure. 
According to Mr. Salter’s determiuation of some specimens from 
Arisaig placed in bis bands by Dr. Honeyman, H. Kniglitii is also 
found at tbat place ; 1 but I bave not met witb any specimens of it. 
The representative of tbis species in tbe Lower Helderberg of New 
York is II. Vanuxemii of Hall. 2 
Botk of tbese species serve to illustrate tbat distinctness of tbe 
Atlantic border area of North America from tbe inland plateau of 
tbe continent, on wbicb I bave elsewhere remarked. 3 Botb in tbe 
Upper Silurian and Carboniferous, tbe rocks and fossils of Nova 
Scotia can be more easily correlated with tbose of Great Britain 
than with tbose of New York and Pennsylvania. So mucb did tbis 
fact strike tbe late Mr. Salter tbat be even thought it possible 
to correlate the fossils of tbe Arisaig section witb tbose of indi- 
vidual members of tbe English Upper Silurian.* 
IV. — Is there a Base to the Carboniferous Rocks in Teesdale ? 
A Question for Silurian Geologists. 
By J. E. Dakyns, Esq. ; 
Of H. M. Geological Surrey of England and Wales. 
D ÜRING a recent excursion into Teesdale I paid a visit to certain 
Mica trap-dykes discovered by my friend Mr. W. Gunn, and to 
a section of tbe Carboniferous beeis below tbe Wkin Sill of Falcon 
Clints, near Caldron Snout, wbicb suggested tbe question whetber 
tkere is not a base to tbe Carboniferous beds in tbat part of Teesdale. 
The section below tbe Wbin Sill bas, I believe, been described by 
Sedgwick. Suffice it to say tbat tbe lowest bed tbere exposed at 
the very foot of tbe crags, just above tbe alluvium of tbe Tees, is a 
breccia tbat reminds one, who knows tbe beds, of the breccia so 
often found at tbe base of the Carboniferous in Yorksbire. The 
next section seen in going down tbe stream is at the old Pencil Mill, 
on tbe banks of tbe Tees below Cronkley Scar. Here tbe beds, 
wbicb were once wrought for slate pencils, consist of bardened 
1 Honeyman, Geol. Journal, vol. xx. 2 Palscontology of New York, vol. iii. 
3 Acadian Geology and Story of tke Eartk. * Honeyman, l. c. 
