Strata super strata: the stratigraphy of Thomas Wright of Durham (1711–1786)

Abstract. The stratigraphic ideas found in a late eighteenth-century manuscript of the English cosmologist, Thomas Wright of Durham, are described and discussed in the context of the development of his contemporaries’ ideas concerning the age of the Earth and formation of its rock strata. Wright, a convinced Plutonist in his explanation of the volcanic origin of horizontal strata, invoked the earlier concept of vegetative growth of minerals as a way of accounting for inclined strata. Mountains grew from small stones and emerged from the sea, pushing initially horizontal volcanic strata into inclined or vertical orientations. In emerging, they acquired a layer of shells of marine animals, which subsequently were located on the tops of mountains. Through assessment of the degree of petrification, Wright concluded that the age of the Earth was substantially greater than a few thousand years. His thesis that the Solar System represented planets at different stages of evolution through time, Saturn being the youngest and Mercury the oldest, implied to him that at least 10¹² years was necessary for completion of the cycle from creation to destruction of a planet, including the Earth. Wright’s model of the origin and evolution of the Earth was heavily influenced by the writings of Burnet and Whiston, but the stratigraphic ideas were drawn from later debates on the origin of strata and their fossils. The manuscript precedes the publication by James Hutton of observation of unconformities and their implication for the age of the Earth. It provides a fascinating insight into the mind of a second-tier scientist, who nevertheless was party to the ferment of ideas in circulation prior to Hutton’s paradigm-changing paper.