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These concretions have a straight cleavage in the direction of their short axis, and are often coated by fibrous calc-sinter and calcedony.

They are for the most part incrusted with calc-sinter; and the rounded blocks of gneiss, which have all the outward appearance of solidity, have been so disintegrated by the carbonic acid as readily to fall to pieces.

As far as he was able to travel inland, the surface was p. 21composed of secondary limestone, partially covered with a thin layer of calc-sinter. 

On this also depends the formation of stalactites and calc-sinter.

The hollows in some of the fragments of vesicular lava of which the breccias and conglomerates are composed are partially filled with calc-sinter, being thus half converted into amygdaloids.