82 HISTORY OF GEOLOGY AND PALEONTOLOGY. 



Engineer Corps, the duty of preparing the topographical map 

 of the Harz was entrusted to him. From this beginning, 

 Lasius became interested in the structural relations, and 

 prepared a work which was published in two volumes, 

 Observations on the Harz Mountains^ together with a petro- 

 graphical map and a section (Hanover, 1789). 



In the first volume, Lasius describes the "primitive rocks" 

 (Ur-gebirge) and the "vein-series" (Gang-gebirge), &n& places 

 these groups in contradistinction to the " Flotz formations " or 

 younger stratified deposits. The "vein-series" comprises 

 marine limestones with corals, orthoceratites, bivalves, and 

 gastropods ; slates, greywackes, and sandstones ; trap-rock, 

 porphyry, and serpentine. The distribution of the various 

 kinds of rock is entered with great accuracy upon a coloured 

 petrographical map, and the term greywacke is used for the 

 first time in the literature for a sandstone made up of finely 

 fragmental granite debris. 



Lasius follows Lehmann for the most part in his sub-divi- 

 sions of the Flotz deposits ; he shows, however, that a part of 

 the porphyry occurs in association with the Red Sandstones of 

 Permian age, and must therefore be younger than the main 

 body of the vein series. 



The second volume of the work is devoted to a description 

 of the ores and minerals in the Harz mountains, and contains 

 many new and valuable observations. 



The Thuringian Forest was made the subject of several 

 excellent geological works by an eminent scholar of Werner, 

 Johann Karl Wilhelm Voigt (1752-1821). Trained for the law, 

 Voigt gave up this profession, became an ardent geologist, 

 and held the post of Councillor of Mines at Ilmenau in 

 Thuringia. 



Voigt's work, in two volumes, entitled Mineralogical Journey 

 through the Duchy of Weimar and Eisenach, was published 

 between 1781 and 1785. Like many of his contemporaries, 

 Voigt wrote this work in the form of letters. It contained 

 what was at the time rather exceptional, a series of geological 

 sections. Another work, which was undertaken by Voigt at 

 the desire of Bishop Henry, gives a mineralogical description 

 of the district around the monastery of Fuld. The basalt and 

 phonolite rocks in the neighbourhood are accurately entered 

 in a coloured geological map, and the text is remarkable for 

 Voigt's tacit renunciation of Werner's views about the origin 



