Autograph letter signed.
12 mo. 3 pp. on bifolium. In French.
Highly interesting scientific letter on xyloid lignite as a geological stratum, very likely addressed to the French chemist, mineralogist, and geologist Alexandre Brongniart (1770-1847). Humboldt first announces the enclosure of an article on fossil forests in Russia by the Russian philosopher and jurist Aleksandr Kunizyn, as he sees many connections to the recipient's work. He then asks the recipient for "just six lines" on xyloid lignite for his "tableau géologique", specifically "the location and extent it occupies, the thickness of the lignite layer", adding some hypotheses of his own: "If you think this is older than the chalk, then it is older than the ball clay with lignite on top of the chalk. Are not your lignites immediately superimposed on the Jura limestone and the oolitic and marly limestone formations placed between the alpine limestone and the chalk?" Humboldt also points to the recent discovery of the geologist Constant Prévost of "lignite underneath chalk" near Caen. Finally, Humboldt asks the recipient where he would place the xyloid lignites within an added sketch of geological strata of the Jurassic, commenting: "I know your lignites are not that common, but you can judge by analogy".
The letter can be dated by a recipient's note "avril-mai 1822" and Kunizyn's article "Holzsteine in Russland. Notice sur les couches de Lignite observées en Russie par le Prof. Kounizin" that was published in the Bibliothèque universelle des Sciences, Belles-Lettres, et Arts, vol. 19 in March 1822. Alexandre Brongniart would publish his important work on xyloid lignite as part of the Dictionnaire des sciences naturelles, vol. 26, in 1823 and the article was published separately later that year as "Des Lignites". Evidently, Humboldt closely followed and supported Brongniart's research on xyloid lignites. In his article, Brongniart mentions that he adopted Humboldt's geographical nomenclature. Beyond Humboldt's "Esquisse d'un tableau géologique de l'Amérique méridionale" (1801) no publication of a geological table was finalized.