VAEEOLITIC DIABASE OF THE FICHTELGEBIRGE. 59 



Oelschnitz, as at Berneck and near Stein. This gives us a maximum 

 age. The intrusion was apparently before the great earth-movements 

 in which the band of Palseozoic sediments that now occupies the 

 valley from Berneck through Gefrees and Sparneck to Schwarzen- 

 bach was squeezed in between the Miinchberg gneiss and the 

 igneous rocks of the Fichtelgebirge. 



The normal strike of the Devonian was no doubt originally 

 parallel to that of the Silurian and Cambrian and to the valley : 

 but the mass of the hard diabase has resisted comjjression better 

 than the more yielding sediments, and these have been bent round 

 the diabase until their strike is often very oblique to their original 

 direction. Further, the fact that the diabase is faulted against the 

 gneiss on the other side of the Oelschnitz suggests that the diabase 

 was consolidated before the great earth-movements took place which 

 impressed upon this area its principal features. 



YI. The Oeioix of the Yariolitic Structure. 



In this examination of the diabase to the south of the Oelschnitz we 

 have seen that the variolite in a more or less perfect form constantly 

 tends to appear along the lines of contact with the neighbouring 

 rocks, or where the diabase becomes spheroidal. It was this relation 

 of the variolite to the neighbouring deposits, and a certain resem- 

 blance of the varioles to the baked shales, that led Prof, von Giimbel 

 to the theory that these bodies were fragments of the Devonian 

 rocks caught up at the time of intrusion. The detailed microscopic 

 descriptions by Prof. E-osenbusch clearly demonstrate that, except 

 possibly in one case, the varioles are true sphgrulites. Nevertheless, 

 as Prof, von Giimbel has again stated his theory in his latest 

 work *, it may be worth while to note what light is thrown upon it 

 hy field work. Included fragments of the neighbouring shales in 

 the diabase do occur, as is shown by a good specimen in the Heidel- 

 berg Museum ; but, though baked, these have no resemblance to 

 the true varioles. In all cases in which the varioles were formed 

 of more than mere globulitic accumulations, or which are sufficiently 

 well preserved for their original constituents to be determined, they 

 consist of plagioclase needles, ilmenite, and pyroxene ; the baked 

 schists maj^ be sericitic and chloritic, but the above minerals have 

 not been developed. Moreover, the occurrence of the varioles in 

 bands parallel to and at a little distance from the circumference of 

 the spheroids, their regularity, and the gradual passage of the 

 variolitic into the normal compact diabase by the diminution in size 

 and number of the varioles, are features which cannot be satis- 

 factorily explained on Prof, von Giimbel's hypothesis. In some 

 cases there seems to have been some confusion, here as elsewhere, 

 between the true variolites and the pseudovariolites or spilites. It 

 is sometimes not easy, without the aid of the microscope, to dis- 

 tinguish between the variolite and some of the weathering amyg- 



* ' Geologie von Bayern,' Th. i. Lf. 1 (1884), pp. 78, 79. 



