Geikie does not give the date of the third volume of his work, but it was apparently about 1771, as vol.ii.

was published in 1770.

I copy Geikie's account of Guettard's observations often in his own words.
[70] Lyell's _Principles of Geology_.
[71] Geikie states that the doctrine of the origin of valleys by the erosive action of the streams which flow through them, though it has been credited to various writers, was first clearly taught from actual concrete examples by Desmarest._L.

c._, p.

65.
[72] Jameson's _Cuvier's Theory of the Earth_, New York, 1818.
[73] J.G.Lehmann of Berlin, in 1756, first formally stated that there was some regular succession in the strata, his observations being based on profiles of the Hartz and the Erzgebirge.