He was deeply impressed to see the workers breaking large bars out of steep walls of rock and filling the valley with thunder . greywacke becoming gravel through massive hammer strokes 當(dāng)時,工人們震天動地從巖壁上取下巨石以及用錘把硬砂巖敲打成碎石的情景給他留下深刻的印象。
百科解釋
Greywacke or Graywacke (German grauwacke, signifying a grey, earthy rock) is a variety of sandstone generally characterized by its hardness, dark color, and poorly sorted angular grains of quartz, feldspar, and small rock fragments or lithic fragments set in a compact, clay-fine matrix. It is a texturally immature sedimentary rock generally found in Palaeozoic strata.