perforata, Hind, Q. J. Geol. Soc. Lond. Vol. 46, Feb., 1890,
page 59, plate 6, fig. 1, natural size, showing irregular growth
and perforated walls; 2, another Bpecimen; 3 (X 2) cross sec-
tion; 4 (X 20) cross section of wall plates, showing it com-
posed of globate spicules; 6 (X 60) several globate spicales
dissolved out; 6 (X 200) a spicule greatly magnified; 7, iUsar-
face maffni/ied 660 times linear ; S, one enlarged iOO times to
show the radial fibres ; 9, one (X iOO] corroded on surface, and
inside filled with banded chalcedony; 10, one (X 200) with re-
placed core, but unchanged surface. " These sponges furnish
additional proof the connection between these organisms and
beds of chert BnA silica (other than quartz). Thus, in the Oliff at
Scarborough, as Mr. Hudleston has shown, there is in the Lower
calcareous grit, from which these sponges have been obtained,
a bed 3^ feet of intensely hard chert, and beneath this, thirty
feet of catc. grit largely cemented with silica. There can be
little doubt that most of the silica in this considerable thick -
ness of rock (not reckoning the sand grains) is due to the
siliceons gouges. * • • Where the minute globates are
not themselves now present, they are represented by minute
empty molds," etc. (Hinde).
