Of all English geologists, Mr. Sorby has been at once the most indefatigable and the most successful in the study of the microscopic structure and metamorphic conditions of rocks. The brief abstract furnished us by the Geological Society, which we print at p. 231, gives but little idea of the importance of the paper Mr. Sorby read last month. It gives, it is true, the pith of the subject, but so short and inexplanatory a paragraph is not likely to attract such attention as the paper deserves. Those who have the pleasure of Mr. Sorby's acquaintance know how persistently he works at anything puzzling which comes in his way. He never leaves it until he has got to the solution of the riddle. It happened some time ago, when in Germany, at the meeting of savants at Speyer, on which occasion he transmitted an account of the proceedings, with some notes on meteorites and sponges (see Vol. IV. p. 501), that Professor Blum presented him with a specimen of the singular conglomerate known as the “nagel-flue.” This conglomerate, which occurs in some places in Switzerland, consists of hard limestone pebbles, the ends of some being impressed into the substance of others,—a condition hitherto inexplicable, although Blum, Von Dechen, Escher von der Linth, Nöggerath, Daubrée, and others have essayed opinions and suggestions, some of them attributing the impressions to merely mechanical, others to purely chemical action.