344 COSMOS. 



ries of Zumbalica, but I have found black obsidian with a 

 conchoidal fracture in very large masses, immersed in bluish 

 gray weathered perlite, amongst the blocks thrown out 

 from Cotopaxi and lying near Mulalo. Of this, fragments 

 are preserved in the Royal Collection of Minerals at Berlin. 

 The pumice-stone quarries here described, at a distance of 

 sixteen miles from the foot of Cotopaxi, appear therefore, 

 to judge from their mineralogical nature, to be quite fo- 

 reign to that mountain, and only to stand in the same 

 relation to it, which all the volcanoes of Pasto and Quito, 

 occupying many thousand square miles, present to the vol- 

 canic focus of the equatorial Cordilleras. Have these 

 pumice-stones been the centre and interior of a proper 

 crater of elevation, the external wall of which has been 

 destroyed in the numerous convulsions which the surface 

 of the earth has here undergone ? or have they been depo- 

 sited here upon fissures in apparent rest, during the most 

 ancient foldings of the earth's crust ? For the assump- 

 tion of aqueous sedimentary alluvia, such as are often exhi- 

 bited in volcanic tufaceous masses mixed with remains of 

 plants and shells, is attended with still greater difficul- 

 ties. 



The same questions are suggested by the great mass of 

 pumice-stone, at a distance from all intuniescent volcanic 

 platforms, which I found on the Rio Mayo in the Cordil- 

 lera of Pasto, between Mamendoy and the Cerro del Pul- 

 pito, 36 miles from the active volcano of Pasto. Leopold 

 von Buch has also called attention to a similar perfectly 

 isolated eruption of pumice-stone described by Meyen, which, 

 consisting of boulders, forms a hill of 320 feet in height, 

 near the village of Tollo, to the east of Valparaiso, in Chili. 

 The volcano Maypo, which upheaves Jurassic strata in its 

 rise, is two full days' journey from this eruption of pumice- 

 stone **. The Prussian Ambassador in Washington, Fried- 

 rich von Gerolt, to whom we are indebted for the first 



35 "The volcano of Maypo (S. lat. 34 150 which has never ejected 

 pumice-stone, is at a distance of two days' journey from the ridge of 

 Tollo, which is 320 feet in height and entirely composed of pumice- 

 stone, inclosing vitreous felspar, brown crystals of mica, and small 

 fragments of obsidian. It is, therefore, an (independent) isolated erup- 

 tion, quite at the foot of the Andes and close to the plain." Leop. de 

 Buch, Desc. Phys. des lies Canaries, 1836, p. 470. 



