Freshwater calcium carbonate.
1 The formation is soft calcareous tufa , such as forms the bottom of all this basin.
2 The valley, which gradually widens, is bordered with hills of calcareous tufa , called here tierra blanca.
3 The fossil bones which lie in the calcareous tufa of this region will yet, we hope, reveal the ancient fauna.
4 Formed of calcareous tufa
5 These rocks, in the southern part of the country especially, are often covered with twelve or fifteen feet of soft calcareous tufa .
6 "It's calcareous tufa I'm a-wearing, wove on me by exudation and accretion in the past two thousand years."
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