Geological Society of London. 89 



or no room for Millstone Grit to be bi-ouglit down to the surface. 

 Nor has the author succeeded in finding any sign of this rock on the 

 Somersetshire side. 



Owing to the fact that softer Upper Limestone Shales are brought 

 down by the fault, its westward extension may be traced by a line 

 of depression resulting from the greater ei'osion of these softer beds. 

 In the map which the author exhibited, a triangular wedge of 

 Upper Limestone Shales, brought down by the fault, had its apex 

 near Hill Farm (see Survey Map), and its base abutting on the 

 Triassic beds south of Durdham Down. If the fault do not tend to 

 die out westwards, the apex of this triangle must be placed further 

 S.W., for which there is no evidence, while there is some against it. 

 The southern side of the triangle marks the line of fault. Further 

 west the author believed that evidence exists of the faulting-down 

 of a wedge of Mountain Limestone into the Lower Limestone Shales. 



2. " On the Recent Discovery of Pteraspidian Fish in the Upper 

 Silurian Rocks of North America." By Prof. E. W. Claypole, B.A., 

 B.Sc. London, F.O.S. 



The fossils now described from Pennsylvania are the first authentic 

 remains of fishes found in the Silurian rocks of America, and some 

 of them are the oldest undoubted vei'tebrates yet discovered. Pre- 

 viously fish had not been detected in America below the Devonian 

 Corniferous Limestone of Ohio, and the Lower Devonian of Canada. 



The most important fish-remains hitherto known from beds of 

 Silurian age are from the bone-bed of the Upper Ludlow rocks, one 

 specimen, the oldest in Europe with the exception of Pander's 

 doubtful Couodonts, having been recorded from the Lower Ludlow. 

 The fossils now described are closely allied to the two Ludlow types 

 and consist of the spines known as Onchus, and the shields referred 

 to Scaphaspis and belonging to the peculiar family Pteraspidee. 



The author entered into a detailed comparison of the English 

 Silurian Pteraspids as described by Professors Huxley and Ray 

 Lankester, and those now discovered in America. He described the 

 three layers of which the shields of the Pennsylvanian Pteraspids 

 are composed, and proposed for their reception a new genus, Falce- 

 aspis. He considers the Pteraspid83, in which no bony structure 

 has been detected, a distinct family from the Cephalaspidse, which 

 exhibit that structure. 



He then proceeded to correlate the American beds yielding Palce- 

 aspis with the Ludlow beds of England. The American fish were 

 chiefly found in the Bloorafield Sandstone at the top of the middle 

 division or variegated shale of the fifth group of Rogers. This 

 fifth group of the Pennsylvanian Survey immediately underlies the 

 Water-lime, corresponding to the English Lower Ludlow, and has 

 been shown by the writer to represent the Onondaga shale of New 

 York. The position of the latter in the series is shown by the 

 following sections taken from Prof. James Hall : — 



New York. Great Britain. 



Lower Helderberg Wanting. 



AVater-lime Lesmahago beds. 



Onondaga salt group Wanting. 



Niagara group Wenlock Limestone. 



