Yards of thickness. "Chalk 120 Golt 50 Sand of Bedfordshire 10 to 20 Northamptonshire lime and Portland lime, lying in several strata 100 Lyas strata 78 to 100 Sand of Newark about 30 Red Clay of Tuxford, and several 100 Sherwood Forest pebbles and gravel 50 unequal Very fine white sand uncertain Roche Abbey and Brotherton limes 100 Coal strata of Yorkshire --" The order of succession of the Cretaceous, Jurassic, Triassic and Permian beds will be readily recognised as indicated in this section, though the discovery of the detailed succession of the Jurassic rocks was reserved for Smith. In the year 1778, John Whitehurst published _An Inquiry into the Original State and Formation of the Earth_, containing an Appendix in which the general succession of the strata of Derbyshire is noted. The main points of interest are that the author clearly recognised the 'toad-stones' of Derbyshire as igneous rocks, "as much a _lava_ as that which flows from Hecla, Vesuvius, or Ætna," though he believed that they were intrusive and not contemporaneous, and he also foreshadows the distinction between the solid strata and the superficial deposits,--"we may conclude," he says, "that all beds of sand and gravel are assemblages of adventitious bodies and not original _strata_: therefore wherever sand or gravel form the surface of the earth, they conceal the original _strata_ from our observation, and deprive us of the advantages of judging, whether coal or limestone are contained in the lower regions of the earth, and more especially in flat countries where the _strata_ do not basset."