ON ITS EXTEEIOR. VOLCANOES. 219 



to measure their temperature, warns the observer not to 

 linger. The temperature of the sulphureous vapours 

 was 117*7, that of the air 69, and that of the " sulphur 

 rivulet," which, perhaps, in its upper portion may be 

 cooled by the snow-water from the volcano of Tolima, 

 84-6. The mica-slate which contains pyrites is inter- 

 spersed with sulphur in pieces. The sulphur prepared 

 for sale is obtained chiefly from an ochrous-yellow clay 

 mixed with native sulphur and weathered mica-slate. 

 The labourers (who are Mestizos) suffer in their eyes 

 and muscles. When Boussingault visited the Azufral de 

 Quindiu, 30 years later, in 1831, the temperature of 

 the vapours (which he analysed chemically) ( 302 ) had 

 diminished so much that it was actually below that of 

 the free air, the latter being 7l-6, while the former was 

 from 66*2 to 68. The same excellent observer saw, in 

 the Quebrada de Aguas calientes, the locality where 

 the trachyte of the adjacent volcano of Tolima breaks 

 through the mica. The also eruptive black trachyte of 

 the volcano of Tunguragua was distinctly seen by myself 

 covering the garnetiferous greenish mica-schist, near the 

 rope bridge of Penipe. As sulphur had not previously 

 been seen in Europe in what were formerly called 

 '" primitive rocks," but only in tertiary limestone, gyp- 

 sum, conglomerates, and in true volcanic rocks, its oc- 

 currence in the Azufral of Quindiu (N. lat. 4-^) is note- 

 worthy, and the more so, because it is repeated south of 

 the equator, between Quito and Cuenca, on the northern 

 declivity of the Paramo del Assuay. In the Azufral of 

 Cerro Cuello (S. lat. 2 13') I saw, also in the mica-slate, 

 at a height of 7980 feet, a very considerable bed of 

 quartz ( 303 ) richly interspersed with sulphur. At the 



