by blasting, and by the presence of the workmen, the ice would be perennial.  Humboldt[166] speaks of the ice in these mines and on the Sauberg.  Reich states that ice is found in the mill-stone quarry of Nieder-Mendig, quoting Karsten’s Archiv fuer Bergbau.[167] The ice is found in the hottest days of summer, although the interior of the quarry is connected with the outer air by many side shafts.  The porous nature of the stone is assigned as the cause of the phenomenon.  Daubeny (On Volcanoes) describes the remarkable basaltic deposits at Niedermennig—­as he spells it—­but says nothing of the existence of ice.

Daubuisson[168] speaks of a Schneegrube, on a summit of the Riesengebirge, in Silesia, 4,000 feet above the sea; but such holes are common enough at that elevation, and I have seen two or three remarkable instances on the Jura, within the compass of one day’s walk.  Voigt[169] describes an Eisgrube in the Rhoengebirge, on the Ringmauer, the highest point of the Tagstein, where abundant ice is found in summer under irregular masses of columnar basalt.  Reich had received from a forest-inspector an account of an ice-hole in this neighbourhood, called Umpfen, which is apparently not the same as that mentioned by Voigt.

In the Saxon Erzgebirge there are three points remarkable for their low temperature,[170] in addition to the mines on the Sauberg mentioned above.  These are the Heinrichssohle, in the Stockwerk at Altenberg, where the mean of two years’ observations gives the temperature 0 deg..54 F. lower at a depth of 400 feet than at the surface; the adit of Henneberg, on the Ingelbach, near Johanngeorgenstadt, where the temperature was again 0 deg..54 F. lower than in shafts some hundred feet higher; and the Weiss Adler adit, on the left declivity of the valley of the Schwarzwasser, above the Antonshuette.  It would appear that there are local causes which affect the temperature in the Erzgebirge, for Reich found that in several places the mean temperature of the soil was higher than that of the air:  for instance—­

Soil.  Air.  Height above the sea.

Altenberg       ...   42.732 deg.  Fahr.  41.27 deg.     2,450 feet
Markus Roehling  ...   43.542 deg. "      41.832 deg.    1,870”
Johanngeorgenstadt.   43.115 deg. "      41.09 deg.     2,460”

The temperature at Markus Roehling is peculiarly anomalous, considering the elevation of the surface above the sea.

There is said to be an ice-cave in Nassau, but I have been unable to obtain any account of it, unless it be the same as the ice-field mentioned on page 303.