RT SS 
264 STRUCTURAL AND FIELD GEOLOGY 
often in convulsed attitudes. The same phenomena are encountered in 
the famous lithographic limestone of Solenhofen, in the Tertiary deposits 
of Monte Bolca, and even in the marl-slate of England, which is on the 
same geological horizon as the copper-slate of Mansfeld, but which, 
unlike the latter, contains no copper-ore. The sudden descent to the 
sea of a large volume of fresh water sometimes results in the wholesale 
destruction of fishes. Thus, in January 1857, an immense body of fresh 
water, descending by subterranean courses, was suddenly discharged 
upon the sea-floor off the coast of Florida. So great was this discharge 
that the saltness of the sea was sensibly diminished, and myriads of dead 
fish floated on the surface and were strewn along the shore. Again, 
earthquake shocks have sometimes been equally destructive. During 
the Indian Earthquake of 1897, for example, fishes were killed in myriads 
as by the explosion of a dynamite cartridge, and for days afterwards the 
river Sumesari was choked with their dead bodies. That similar results 
must have attended earthquake shocks in earlier ages cannot be doubted. 
As the sudden destruction and entombment in mud of large numbers of 
fish may be due either to sudden freshening of salt water or to earthquake 
shock, it is obvious that the abundant fish remains of the Mansfeld 
copper-slate cannot be cited in support of the view that they were 
poisoned by metallic solutions. It would seem more probable, therefore, 
that the ores by which they are encrusted are really epigenetic, or 
subsequent introductions. Further, it must be noted that the ore- 
formations in question are not confined to the bituminous slate, but are 
met with also in numerous fissures which pass upwards into the overlying 
Zechstein ; and it has been observed that the percentage of ore contained 
in the copper-slate itself increases as it approaches those fissures. It 
is remarkable that the Permian system, all the world over, is apt to 
show impregnations of copper-ore. Towards the close of that period 
crustal movements seem to have affected wide areas, while volcanic action 
was displayed in many regions. Possibly, therefore, it was during this 
period of subterranean activity that the strata were traversed by copper- 
bearing solutions ascending from below. 
4. CONTACT ORE-FORMATIONS 
Under this head are included sheets, irregular masses, 
ramifying veins and threads, etc., occurring in rocks usually at 
or near their junction with plutonic masses. These ore- 
formations (Fig. 107) include iron oxides and sulphides, and 
frequently also ores of copper, lead, zinc, tin, arsenic, antimony, 
mercury, etc.; and, in some cases, gold and silver. They may 
occur at or very close to the junction-line—particularly when 
the rocks surrounding the igneous mass are much broken 
and jumbled; or they may be met with at the surface for a 
mile or more away from an igneous batholith, but seem never 


+ aaa Mille aapects certs * % AE YR Sh ew Oe ae oe 
