Geology of the Harz Mountains. 251 



and as tliere is reason to suppose that all the fissures running 

 parallel to the present edge of the Harz are of the same age, 

 it follows that these fissures were in existence before the 

 quartz-porphyries of the Eothliegendes period were erupted. 

 The fissures must thus be of Carboniferous age, as they were 

 formed between the great Upheaval and the Permian period.^ 

 They cross the Clausthal plateau from west to east, and 

 although not known to be quite continuous, are represented 

 by the system of fault veins which Kayser has traced across 

 the Bruchberg to the Andreasberg district. These faults all 

 cut through the granite wherever it comes in their way, and 

 thus prove conclusively that it too is of Carboniferous age. 

 The granite must have been quite hard and crystalline 

 when the faulting took place, otherwise the fissures could not 

 have remained open for the passage of metallic solutions. 



The absence of granite fragments from the Carboniferous 

 and Permian conglomerates is probably due to the fact that 

 the granite masses at that time lay buried underneath sedi- 

 mentary strata, and had not been exposed by denudation 

 when the whole region became submerged. 



Fragments of the Culm rocks are also unknown in the 

 conglomerates of Ilfeld, but their absence is no proof that the 

 Lower Harz was never covered by Lower Carboniferous 

 rocks. The highest rocks would be carried off first and de- 

 posited in the deepest parts of the adjacent sea bed, and if 

 Culm strata were present they would first be removed from 

 this area. The eastern portion, if not the whole of the 

 ancient Harz, must have remained above sea-level throughout 

 the greater part of the Coal-measure period, during which the 

 Culm may have been completely removed and laid down, 

 perhaps at a great distance from the present base of the 

 mountains. It is also possible that the Culm may not have 

 been so thick in the eastern area as on the Upper Harz, and 

 may have been eroded away comparatively soon, laying bare 

 the underlying Devonian series, the greater part of which 

 was also denuded off before the Permian period. 



The preservation of the Culm of the Clausthal plateau is, 



^ E. Kayser, "Ueber die Quarzporphyre der Gegend von Lauterberg im 

 Harz" (Jahrb. d. k. pr, Landesanst, 1880, p. 45). 



