Dr. G. J. Hinde—Spitzbergen Chert-Deposits. 245 
resembling those of Doryderma Dalryense,' H. (PI. VIII. Fig. 13), from 
the Carboniferous of Ayrshire, and minute hexactinellid spicules 
(Pl. VII. Fig. 12). Both the forms of the spicules and the mineral 
structure of the rock point to the conclusion that the pebble has 
been derived from some of the cherty sponge-beds of the Permo- 
Carboniferous series. 
The character of these chance fragments from the Productus-chert 
division of the Permo-Carboniferous series distinctly shows that the 
chert beds in this division are largely composed of the detached 
spicules of disintegrated siliceous sponges, and thus of organic origin 
in the same manner as the chert-beds in the Yoredale Series of 
Yorkshire, North Wales, and Ireland. Not only is the general 
character of the rock extremely similar, but in some instances the 
same forms of spicules are present in the Spitzbergen, as in the 
British rocks. The dark siliceous schists, on the other hand, inter- 
calated between the cherts, are chiefly composed of minute grains 
of quartz, and thus merely of sedimentary origin, but in some of 
these sponge spicules are also numerously represented. It is true 
that the number of specimens of chert available for examination is 
very few, and they might be regarded as insufficient of themselves 
to warrant the conclusion that this great thickness of rock, which 
at one locality on Axel’s Island reaches 870 feet, is due to the 
accumulation of the skeletal débris of siliceous sponges; but taking 
into consideration the fact that beds of similar cherty rock, which in 
Yorkshire? have an estimated thickness of 90 feet, and in North 
Wales of 350 feet, can be proved to be due to sponge remains, 
there is nothing extravagant in the supposition that this much 
greater thickness of rock has had a similar origin. It is reasonable 
to suppose, moreover, that if specimens collected indiscriminately 
thus show their derivation from sponge remains, still stronger 
evidence would be obtainable if search were specially made for it. 
So far as I am aware, the Spitzbergen chert beds have never been 
specially studied; the principal notice of them which I have seen is 
by Baron A. E. Nordenskidld,? who writes of them in 1876 :—“ In 
Ice and Bell Sounds, as well as in Hinloopen, the Spirifer Lime- 
stone and gypsum are covered by a statum of impure limestone rich 
in silica, or by a black flint extraordinarily rich in fossils, especially 
in Producti of large size and with large shells. Within this division 
the flint strata of silica are scarcely ever of the nature of sandstone, 
but form beds, several hundred feet thick, consisting of a nearly pure 
flint, and I think it highly probable that the formation of these 
immense flint beds stands in connexion with the eruptions whence 
originated the massive layers of plutonic rocks which meet us every- 
where on Spitzbergen, and which in many places form the very 
boundary between the Mountain Limestone and the overlying strata 
belonging to later formations.” From this it would appear that an 
1 British Fossil Sponges, pt. i. pl. v. fig. 72, Pal. Soc, vol. for 1886. 
2 British Paleozoic Sponges, pt. ii. Pal. Soc. vol. for 1887, p. 100. 
8 Sketch of the Geology of Ice Sound and Bell Sound, Spitzbergen, Grou. Mac. 
Dec. II. Vol. III. 1876, p. 66. 
