In Poggendorff's _Annalen_ (1841, Erganzsband, 517-19,--Boué, an old offender in that way, says 1842) there is an account of ice being found in the Westerwald, near the village of Frickhofen at the foot of the _Dornburg_, among basaltic débris about 500 feet above the sea.[205] Commencing at a depth of 2 feet below the surface, the ice reaches from 20 to 22 feet farther down, where the loose stones give place to dry sand. The ice is in thin layers on the stones, and is deposited in the form of clear and regular hexagonal crystals. The lateral extent through which this phenomenon obtains is from 40 to 50 feet each way, and is greater in winter than in summer. As in other cases that have been noticed in basaltic débris, the snow which falls upon the surface here is speedily melted. The _Allgemeine Zeitung_ (1840, No. 309), from which the account in Poggendorff is taken, suggested that the melted snow-water which would thus run down among the interstices would readily freeze below the surface, while the heavy cold air of winter would be stored up at the lower levels, and the poor conducting powers of basaltic rock[206] would favour its permanence through the summer. The temperature of the cold current which was perceptible in the parts of the mass of débris where the ice existed was 1° R. (34°·25 F.). Nothing but a few lichens grow on the surface of the débris. These are, I think, all the references I have met with to the prismatic structure of subterranean ice. But there is an interesting account in Poggendorff 's _Annalen_,[207] by a private teacher in Jena, of the crystalline appearance of ice under slow thaw near that town. In the winter of 1840, the Saale was frozen, and the ice remained unbroken till the middle of January, when the thermometer rose suddenly, and the river in consequence overflowed the lower grounds, and carried large masses of ice on to the fields, where it was left when the water subsided. On the 20th of January the thermometer fell again, and remained below the freezing point till the 12th of February: some of the ice did not disappear till the following month.