614 PEOF. W. J. SOLLAS ON THE ESTUARIES OF 



cyatholith type so common in adjacent seas and in the Atlantic 

 ooze ; Foraminifera of various species, such as Miliola, which are 

 usually small and scarcely if at all distinguishable from the young 

 of Miliola obesa figured by Max Schultze (Org. der Porythalamien, 

 plate ii.), Textularia, probably T. variabilis, but more than one 

 species is present, Nonionina crassula, Polystomella umbilicata, Rota- 

 lia, sp., Spirillina, sp., and others, including some finely arenaceous 

 forms ; spicules of Alcyonaria rarely ; fragments of Echinoderm 

 skeletons and minute spines ; and triradiate spicules of Calcisponges, 

 probably derived from Sycandra ciliata and S. compressa. Most of 

 the Foraminifera are quite empty, glassy and transparent; but some 

 contain a brownish soft granular material ; and in one instance a 

 small Eotaline form was observed partially replaced by pyrites. 



The siliceous constituents are chiefly sponge-spicules, very rarely 

 Radiolaria, and a variable quantity of Diatoms. The sponge-spicules 

 are of very various forms and sizes. They include : — simple acerates, 

 some smooth like those of Amorphina panicea, others entirely 

 microspined, like those of Hymeclesmia injlata ; simple acuates ; 

 acuates with a pin-like head, some of whichmay have been derived from 

 Cliona, and others from Suberitis ficus and other Suberites ; small 

 acuates entirely microspined, similar to the echinating spicules of some 

 species of Dictyocylindrus. and others similar to the smaller acuates 

 of Microciona armata ; large pin-headed acuates with the head only 

 spined, similar to the large spicules of Microciona armata ; large 

 trifid spicules with simple projecting rays, probably derived from a 

 Geodine sponge ; and others with expanded bifid rays somewhat 

 similar to those of Eccionema ponclerosa ; Geodine globates and 

 stellates of Tethya lyncurium ; in one instance a bihamate, such as 

 might have come from Halicliondria inomatus. Though many of the 

 spicules are entire, the majority are mere fragments, little rod-like 

 cylinders of very various lengths and thickness, perforated by an 

 enlarged axial canal. 



From the inorganic constituents but little is to be learned, least of 

 all from the mud ; the fragments of quartz are more interesting, 

 since precisely similar fragments abound in the tributary rivers 

 of the estuary, viz., the Severn, Stratford Avon, and Bristol 

 Avon ; similar quartz grains, however, are common in the cliffs of 

 Aust. 



By far the most remarkable constituents are the remains of or- 

 ganisms ; for these are all marine, and yet occur on the banks of 

 rivers at a great distance from a truly marine area. 



Past experience has shown me that rivers sometimes bear to the 

 sea considerable quantities of undissolved calcareous matter derived 

 from the formations through which they flow ; thus coecoliths and 

 Foraminifera derived from the denudation of the chalk are always to 

 be found floating in the water of the river Cam near Cambridge, 

 and have in past times been deposited along with other sediment in 

 its gravels, as, for instance, near Barnwell, a fact which has led me 

 to suggest* that the corns tones of the Old Bed Sandstone have 

 * Quart. Journ. Geol. Soc. vol. xxxv. p. 492. 



