1884.] Microscopic Structure of some Rods from Ecuador. 135 



the "trachytes" from the Enganean Hills. Under the microscope 

 it is seen, like the last described, to have a clear base with micro- 

 liths of felspar, but scattered in this are numerous rods of iron oxide, 

 and plates of a very ferruginous mica, sometimes all but opaque. 

 There are a few crystals of hornblende in diameter up to about 

 04 inch, which are strongly dichroic. There is but little if any 

 augite. 



One of the two specimens from the rock in situ appeared rather 

 intermediate between the two varieties just described, and as it 

 seemed rather decomposed was not sliced ; the other, in better 

 preservation, resembled the more mottled or streaky looking specimens 

 among the debris, and afforded slight indications of a fluid al structure. 

 This is indicated under the microscope by a "flow" of the microliths 

 rather than by a marked striping or banding. Except for this, the 

 matrix resembles that of the first described, witli some approach to 

 that of the second. There is nothing special to note in the larger 

 felspar crystals which are plagioclastic, similar to those so often 

 described ; some are clear, some rather full of glass enclosures. 

 There are fairly numerous hornblende crystals, some of an olive- 

 green, others of a brown-green colour, strongly dichroic. Some 

 augite crystals are certainly present, and a few of a brown mica. 



Microscopically the specimen from the highest visible rocks on 

 Cayambe barely differs from that just dascribed, except that a fluidal 

 structure is more inconspicuous. The result of microscopic examina- 

 tion is similar, the differences being but varietal ; hornblende, iron- 

 mica, and augite are present, the last being the less conspicuous 

 constituent. 



Thus the rocks of Cayambe are very uniform in character, and of 

 the same general type as those of Chimborazo, Antisana (in part), and 

 Piehincha (in part). They are andesites, but as they contain horn- 

 blende and augite, as well as mica, it is difficult to give them a dis- 

 tinctive name. I am inclined to view the first, and perhaps the third, 

 as minerals belonging to an earlier stage of consolidation than the 

 second : thus perhaps it is more appropriate to classify these rocks 

 with the augite-andesites, using the word hornblendic as a qualifying 

 epithet, except in the case of the second specimen described above, 

 which might perhaps be termed a mica-andesite. 



Corazon. 



" The mountain Corazon lies almost exactly midway between Illiniza 

 (17,400) and Atacatzo (14,892), and its summit is nearly due west of 

 the town of Machachi, and south-south-west of Quito. It has 

 received its name from a resemblance which it is supposed to have 

 to a heart. Though a prominent mountain, it is one of the minor ones 

 of Ecuador. Its height, according to my mercurv barometer observa- 



