Fig. 4. — Diagrammatic representation of the theory. 



Surface of Ice-Slieet. decreasing by thaw 



rn n 



Sponges on Sea-Floor I 



S J\. | J \/ Base of Ice-Slieet. 1 inc reasin g by fr'eezin 



I. The ice-sheet afloat. 

 II. The sheet, having increased by freezing below more than it has lost by 

 thaw from above, now rests upon the sea-floor, freezing-in the sponges. 



III. The same at a later stage. The basin has begun to yield sodium sul- 



phate from the brine, some of which is included in the ice. 



IV. Milder conditions have caused a net decrease in thickness, the sheet 



rising off the sea-floor, taking Avith it the included material. 



