EXCAVATIONS AT DEWLISH. 221 



trench and filled in the pot-holes and channels of the fossil 

 waterfall. It has a harsh gritty feel when rubbed between 

 finger and thumb and, although of such exceedingly fine 

 grain, does not form a good polishing powder, as it scratches 

 metal deeply. It had been described as a quartz sand, but 

 the addition to it of dilute hydrochloric acid causes a brisk 

 evolution of carbon dioxide which reveals the presence of 

 carbonate. This is confirmed when the sand is examined 

 microscopically ; the constituents then seen being in 

 order of abundance (1) prismatic fragments of shell, mostly 

 of Inoceramus, (2) small rhombs of calcite, forming 

 together about three-fifths of the sand ; (3) quartz in 

 small angular crystalline pieces ; (4) small chips of flint ; 

 spicules from sponges constituted the remainder of the sand 

 except for rounded grains of glauconite, and crystals of 

 tourmaline and zircon. 



The rhombs of calcite are minute and resemble some 

 described by the late Russell Gwinnell which were collected 

 from a water tank at Belton, Grantham. This material 

 consisted of a white, glistening, crystalline powder, or a 

 sand-like aggregate of minute crystals. It was deposited 

 in a water-tank into which water was led through an old 

 leaden pipe, over a mile in length, from a spring rising from 

 the basal beds of the Marlstone (Middle Lias) ! The 

 crystals were formed during the passage of the water through 

 the long pipe when the free surface of water was large as 

 compared with its volume. It was formed during the dry 

 summer months of 191 1 when the water was never more than 

 a trickle. Since that season a greater flow of water has 

 occurred and no further deposit of crystals has formed, but 

 only mud. These observations suggest that the formation 

 of the rhombs of calcite is indicative of conditions of drought 

 and thus afford a clue as to the conditions of formation of 

 the crystals of calcite in the Dewlish Sand. There are, 

 moreover, no constituents in the sand which could not 

 have come from the chalk of the neighbourhood. The 

 evidence is therefore in favour of purely local origin of this 



