At this time the whole range of chemical and physico-chemical science was in an extremely imperfect state; and the first steps to a more improved system involved the necessity of clearing away a vast mass of error which encumbered the path to truth. For instance, one of the fanciful ideas, the offspring of the alchemy of the dark ages, which still continued to haunt the regions of science, was the belief of the conversion of water into earth by gradual consolidation. This subject Lavoisier treated in the true spirit of the experimental method, and clearly showed that the pretended conversion was either a deposition of earthy particles, or a sediment arising from the action of the water on the internal surface of the retort. He also laboured on the analysis of the gypsum found in the neighbourhood of Paris, and on the crystallization of salts. He discussed the project of conveying water from L’Yvette to Paris, and the theory of congelation; and to these researches added extensive observations on the phenomena of thunder and the Aurora Borealis. He next directed his attention more especially to mineralogy; and made excursions, in conjunction with Guettard, into all parts of France, endeavouring to form from different districts a complete collection of their characteristic mineral productions. He made advances towards a systematic classification of facts connected with the localities of fossils, which afterwards served as the basis of his work on the revolutions of the globe and the formation of successive strata, of which two admirable abstracts were inserted in the Memoirs of the Academy of Sciences, for 1772 and 1787.