~ pie) Saal . 
a 7 . 
Rate of Niagara Lateral Erosion.—Wright. 143 
The question as to how much protection has been afforded 
by the talus and the growth of vegetation cannot be definitely 
answered. But as our photographs show, the Niagara shale 
has not been protected at all by talus, and only slightly by veg- 
etation; and, indeed, it is doubtful if the trees growing upon 
such a steep slope are any protection in the long run. They are 
all small, and none of them are old. They are uprooted before 
they are old, and thereby loosen the soil to which they cling. 
It is true that the fragments of shale tend to arrange them- 
selves somewhat like shingles on a roof, and so shed the water 
to some extent. But the frosts and the frequent heavy showers 
are constantly disturbing this arrangement. It therefore 
seems entirely within the bounds of probability that the lateral 
erosion of the Niagara shale at the mouth of the gorge has 
proceeded at one-seventh the rate observed at the exposures 
measured, which is one-quarter of an inch per year, or one 
foot in fifty years. This is the amount necessary to accomplish 
the total enlargement in 10,000 years. 
Photograph 1 shows the tunnel which is the starting-point for our 
measurement. The rocks exposed are the lower part of the Clinton 
shale and the upper part of the Medina. 
Photograph 2 shows the exposure of the eastern side of the lower 
end of the gorge as viewed from the Canada side. The exposed sur- 
face of the Niagara shale is well seen, together with the relation of 
the Niagara limestone to the Clinton limestone. 
Photograph 3 gives a closer view of the exposure of the Niagara 
shale between the Niagara limestone and the Clinton limestone, about 
5,000 feet from the tunnel. 
Photograph 4 shows the erosion of the Clinton shale at about 
1,500 feet from the tunnel. 
NOTE ON A NEW XIPHOSURAN FROM THE UP- 
PER DEVONIAN OF PENNSYLVANIA. 
By C. E. BEECHER, New Haven, Ct. 
The species of Prestwichia here described is chiefly inter- 
esting as being considerably older than any known form in this 
genus, and as showing the segmental structure of the cephalo- 
thorax. 
The members of the family Belinuridze seem to have 
reached their greatest development during the deposition of 
the Coal Measures, and a considerable number have been de- 
