Dr. Hans Reck — Fismireless Volcanoes. 61 



Similarly a fissure filled from below with lava or from above with 

 debris would always be distinguishable by the necessarily different 

 structure of the in-filling material compared with the uniform 

 composition of its surroundings, so that after all I can only repeat 

 my first statement : It is therefore here for the first time proved from 

 observation that in this case at least a fissure does not exist under the 

 base of a volcano for a depth of from 300 to 400 metres. 



Professor Schwarz's second theoretical objection is, that, granted 

 there were no line of weakness in the palagonite itself, one might 

 better regard the volcano as the offshoot of a deeper-lying volcanic 

 fissure than to admit it having been formed by piercing its own way 

 up through the earth's crust even from the magma basin whence it 

 derived its lavas. 



There are several reasons which, unfortunately, do not allow me to 

 agree with Professor Schwarz's ideas. Pirst of all I must repeat 

 that there is no fault known in the whole volcanic surroundings of 

 Herdubreid that is proved or even likely to be older than the volcanic 

 activity of the mountain which began after the ice of the last 

 glaciation had long been melted away. 1 At any rate the fractures 

 and dislocations by which the surroundings of Herdubreid sank down 

 for at least 600-700 metres, and left it as a huge mountain block in 

 its old position, are younger than the volcano, for they have dislocated 

 even the youngest outpours from its crater. 



The reason that allowed Herdubreid to keep its old position can 

 only be found in its being a ' Schild', or massive lava volcano, with 

 an axis of solid lava under its central parts, which served as a strong 

 support against the sinking movements of the surrounding crust. 



The volcanic axis piercing the base of the volcano in no place 

 touches the vertical walls of the volcanic 'Horst', so that from this 

 fact it is only probable that the chimney would go down rather 

 perpendicularly, which is also theoretically necessary to assume from 

 reasons which I have given in the above-mentioned papers, and which 

 are based on the symmetry of the shape of the volcano. So that; 

 even if we were inclined to assume an old fissure under the lava- 

 covered surface of the surrounding level plain, the offshoot of the 

 volcano would necessarily have taken place very deep below the 

 surface. 



But why at such a depth should the rising magma suddenly have 

 left the line of weakness which would have led its lavas in the easiest 

 and shortest way up to eruption? I think it will be rather difficult 

 to find sufficient reasons for even a theoretical explanation of this, 

 but there is one more point which seems strongly to negative the 

 assumption of an underground fracture as the conduit for the magma. 



Professor Schwarz assumes Herdubreid to be an offshoot of a volcanic 

 fissure, and adduces as example for the possibility of his opinion 

 Dauhree's well-known experiments on the exploding of dynamite in 

 steel shells. He also gives a very interesting example of a "fossil 

 earthquake", as he has termed it, which in its course showed 

 characters of a similar kind. In his latter example single blocks, 



1 Compare also Helgi Pjeturss, Zeitschrift der Gescllschaft f. Erdkunde, 

 1908, pp. 451 ff. 



