NO problem in modern geology stands out with such prominence as the origin of that remarkable group of rocks to which the name of the Crystalline Schists has been given, and to none in recent years has so large a share of the literature of the science been devoted. The question is attacked on all sides. By some observers its solution is sought in laborious investigations of the hilly and mountainous regions where these rocks hold their empire among the grander solitudes of nature. By others the question is studied in the quiet of their own libraries or laboratories with all the resources of modern chemistry and microscopy. Great progress has indeed been made in these various ways. Regarding certain aspects of the problem a general agreement has been arrived at; but there are others as to which the difficulties remain as persistently obstructive as ever. Untersuchungen uber die Entstehung der Altkrystallinischen Schiefergesteine mit besonderer Besugnahme auf das Sachsische Granulitgebirge, &c.” von Dr. Johannes Lehmann. (Bonn: Hochgurtel, 1884.)