The tracheae are minute tubes exhibiting a faint transverse striation which is probably the indication of a spiral fibre.
Rocks scored by glacial ice and showing plain indications of striation, together with thousands of erratic blocks, are found scattered all over Iceland.
In the rapidly moving glaciers of the icefjords this striation is not distinctly visible, being evidently obliterated by the strong motion of the ice masses.
They occasionally exhibit striation and originate from large branched cells, the nucleus and unmodified part of which form conspicuous elements.
Roman glass beads are always drawn out, and nicked off hot, with striation Iengthways; except the large opaque variegated beads which are coiled.