Geology of the Harz Mountains. 247 



has been very intense at that locality, and in addition to 

 altered slates several new minerals, including actinolite and 

 axinite, have been originated. Contact metamorphism is also 

 developed around the granular diabase at St Andreasberg, 

 and Credner's description of its geometrical relations as dis- 

 closed by mining distinctly shows it to be intrusive. 



5. A smooth contact surface between the two rocks is of 

 itself almost sufficient to establish the intrusive character of 

 the diabase. A lava stream has rough and slaggy upper and 

 under surfaces, and not smooth and sharply defined bounding 

 planes like those seen at many places between the diabase 

 and the sedimentary rocks. The mere conformability of a 

 massive rock to the strata surrounding it is not necessarily 

 a proof of its contemporaneity unless the upper and under 

 edges be rough and scoriaceous like those of a true lava 

 stream. 



The same considerations apply generally to the diabases 

 which abound among the Lower Devonian rocks in the 

 southern parts of the Harz, and extend from Stiege, east- 

 wards past Benneckenstein to the vicinity of Sachsa, and 

 southwards to the border of the range near Eodishayn. There 

 is here no tuff, the surrounding rocks are metamorphosed into 

 the green shales described above, and what is still more con- 

 clusive, the diabase patches are shown on the map to cross 

 from one horizon to another without regarding the strike of 

 the sedimentary strata. 



(2.) The diabase in the Goslar shales of the Upper Harz 

 occurs chiefly in isolated patches on the hills between Gos- 

 lar and the valley of the Innerste, It appears protruding 

 through the soil at several places, and forms an oval cap to 

 the Steinberg, a hill which overlooks Goslar from the west, 

 and has a height of about 1-450 ft. There can be little doubt 

 that all the diabase in this district is also intrusive, as it does 

 not conform to the strike of the shales, but rises irregularly 

 through them. A fine section is exposed in a newly made 

 cutting for a forest road along the western side of the Konigs- 

 berg, which forms the south-western shoulder of the Steinberg. 

 The section is at a bend in the road near the top of the hill, 

 which commands a fine view over the wooded valley between 



