Trass.
Tarrass. A volcanic earth, or calcareous tufa, resembling pozzuolana, and found in several districts of
France and
Germany, the theaters of extinct volcanic action; the Vivarais, in the center of
France; at Brohl, near Andernach, on the
Rhine.
Like the
hydraulic cement of
Baiae, it consists of ingredients which enable it to harden under water.
Beithier's analysis is as follows:—
| Trass. | Pozzuolana. |
| Silica | 0.570 | 0.445 |
| Alumina | 0.120 | 0.150 |
| Lime | 0.026 | 0.088 |
| Magnesia | 0.010 | 0.047 |
| Oxide of iron | 0.050 | 0.120 |
| Potash | 0.070 | 0.014 |
| Soda | 0.010 | 0.040 |
| Water | 0.096 | 0.092 |
| —— | —— |
| 0.952 | 0.996 |
