When investigating the constitution of antunite or lime-uranite, I secured an extremely fine specimen (of what was then supposed to be this mineral) from the mine at Falkenstein in the Saxon Voigtlaud. I was puzzled by the low percentage of water and other anomalous results which my analysis of the specimen in question gave. While at work upon the solution of this difficulty, Weisbach's note upon uranocircite or baryta-uranite appeared, Winkler's analysis of the Falkenstein mineral clearly proves that we have in it a pure baryta-uranite—a new species of the uran-mica group. I did not, however, abandon my own researches into the nature of this mineral, for the mode in which the water was held by this mineral remained unknown. If isomorphous with autunite, it might be expected to contain 10 aq. in the molecule, 2 of which would probably be retained at 100° C.