In a vastly remote past, and for a vastly extended period, the mighty deep rolled over the surface of a world inform and void, depositing a sediment of its used up living tenants, the microscopic cases of foraminiferæ, sponges, sea-urchins, husks, and the cast limbs of crustaceans. The descending shells of the diatoms like a subaqueous snow gradually buried the larger dejections. This went on till the sediment had attained a thickness of over one thousand feet. Then the earth beneath, heaved and tossed in sleep, cast off its white featherbed, projected it on high to become the chalk formation that occupies so distinct and extended a position in the geological structure of the globe. The chalk may be traced from the North of Ireland to the Crimea, a distance of about 11,140 geographical miles, and, in an opposite direction, from the South of Sweden to Bordeaux, a distance of 840 geographical miles.