On the occurrence of Calcareous Spar in Basalt-tufa. 163 



as the shells last mentioned, it must be believed that it is the 

 layer of the spar which caused a fracture in the rhombic 

 form in the individual in question. — (Annales des Sciences 

 Naturelles, 1839J 



On an interesting mode of occurrence of Calcareous Spar in 

 Basalt-tufa. By William Haidinger, Esq. F.R.S.E. and 

 Member of the Wernerian Natural History Society. 



Fresh sections have lately been exposed, during the exca- 

 vations carried on near Schlackenwerth, with the view to ob- 

 tain water for the new furnaces of Prince Metternich. In 

 these I lately had an opportunity of observing a mode of oc- 

 currence of calcareous spar, which, on account of the conclu- 

 sions to be deduced from it, is particularly calculated to at- 

 tract the attention of those who investigate the changes which 

 tlie crust of our globe has undergone. I have to thank the 

 kind orders of the Imperial Secretary Dr A. Schmidt, for an 

 extremely interesting series of the specimens, and have also 

 to acknowledge the attention of Mr Kellerman, who forwarded 

 them to me. 



Between the layers of a more or less compact basalt-tufa, 

 there occiu" masses, from whose form and surface it seems evi- 

 dent that they Avere originally trunks of trees. The direction 

 in which they lie is from west to east. They are of various 

 diameters, being generally from one to eight inches thick. 

 The most remarkable circumstance connected veith them is 

 their internal structure, which is displayed when the stems 

 are broken asunder. As they lie between the layers, the in- 

 terior, which was previously filled by the wood, exhibits the 

 phenomenon represented in the wood-cuts, and in which Fig. 

 1 is a transverse, and Fig. 2 a longitudinal section. It is there 

 seen that the interior is replaced by radiated groups of crys- 

 tals, which, proceeding from centres a a, and chiefly from the 

 upper side, extend to the opposite walls. The small quantity 

 of organic matter left behind is deposited in the lower por- 

 tions bhm parallel fibres. 



