can remove with a shovel the fine sand , and likewise the coarse sand and broken rock , into which the rocks have been crushed ; this board can be lowered , so that the mouth thus being closed , the fresh rock thrown in may be crushed with the iron - shod stamps . If an oak block is not available ,…
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![An illustration from Georgii Agricolae De re metallica : libri XII. Quibus officia, instrumenta, machinae, ac omnia deni[que] ad metallicam spectantia, non modo luculentissimè describuntur, sed & per effigies, suis locis infertas, adiunctis latinis, germanicis [que] appellationibus ita ob oculos ponuntur, ut clarius tradi non possint. ; Eiusdem De animantibus subterraneis liber, (1556)](https://img.insideoutlibrary.com/img/200/ia-gri_000033125008455038-433-277.webp)
