TRUE VOLCANOES. 325 



cannot determine. It is also geognostically remarkable that, 

 further to the east, on the road towards the small fortress 

 Perote, the ancient Aztec Pinahuizapan, between Ojo de 

 Agua, Yenta de Soto and el Portachuelo, the volcanic forma- 

 tion of coarsely fibrous, white, friable perlite 18 rises 

 beside a limestone (Marmol de la Puebla) which is probably 

 tertiary. This perlite is very similar to that of the conical 

 hill of Zinapecuaro (between Mexico and Valladolid) ; and 

 contains, bet-ides laminae of mica, and lumps of immersed 

 obsidian, a glassy, bluish- gray, or sometimes red, jasper-like 

 streaking. The wide " perlite district " is here covered with 

 a finely granular sand of weathered perlite, which might be 

 taken, at the first glance, for granitic sand, and which, not- 

 withstanding its allied origin, is still easily distinguishable 

 from the true, grayish white pumice-stone sand. The latter 

 is more proper to the immediate vicinity of Perote, the pla- 

 teau 7460 feet in height between the two volcanic chains of 

 Popocatepetl and Orizaba, which strike north and south. 



When, on the road from Mexico to Yera Cruz, we begin 

 to descend from the heights of the non-quartzose, trachytic 

 porphyry of the Yigas towards Canoas and Jalapa, we again 

 twice pass over fields of fragments and scoriaceous lava : 

 the first time between the station Parage de Garros and Canoas 

 or Tochtlacuaya, and the second, between Canoas and the 

 station Casas de la Hoya. The first point is called Loma de 

 Tobias on account of the numerous upraised, basaltic blocks 

 of lava containing abundance of olivine ; the second simply 

 el Malpais. A small ridge of the same trachytic porphyry, 

 full of glassy felspar, which forms the eastern limit of the 

 Arenal (the perlitic sand-fields) near la Cruz Blanca 

 and Rio Frio (on the western declivity of the heights of 

 las Yigas) separates the two branches of the lava-field 

 which have just been mentioned, the Loma de Tablas, and 

 the much broader Malpais. Those of the country people 

 who are well acquainted with the district assert that the 

 band of scoriae is elongated towards the south-south-east, 

 and consequently towards the Cofre de Perote. As I have 



18 The beautiful marble of la Puebla comes from the quarries of 

 Tecali, Totomehuacan and Portachuelo, to the south of the high 

 trachytic mountain, el Pizarro. I have also seen limestone cropping 

 out near the terrace-pyramid of Cholula, on the way to la Puebla. 



