1884.] Microscopic Structure of some Rocks from Ecuador. 407 



The following analyses of the rocks from Chimborazo are also 

 given by Humboldt, which I quote for comparison with the descrip- 

 tion given by myself in Part III of these Notes. The first of them 

 very probably represents a rock nearly identical with that obtained 

 by Mr. Whymper at 19,300 feet. 



97-88 99-80 



I. -Broken from narrow rocky ridge at 19,194 feet ; S.G. 2'806 

 (Raminelsberg). 



II. Specimen collected at 16,179 feet; S.G. 2'685 (Abich). 

 Certain of these specimens appear to have been re-examined by 



Dr. Artope, and described in an inaugural dissertation published at 

 Berlin in 1872 ; but of it I have only been able to see an abstract in 

 Leonard's " Jahrbuch," 1874, p. 93. In this is given the analysis of 

 a specimen from Pichincha, which, as it is described as having a 

 greenish-black hard ground-mass, must be rather different from any 

 in my collection. It was collected at a height of 15,539 feet; the 

 specific gravity was = 2 '624. 



Si0 2 62347 



A1 2 0g 17-324 



FeO 4-501 



MnO . 0-036 



CaO 5-426 



MgO 3-603 



KO 3-126 



Na^O 4-286 



H O . 0-129 



100-778 



It will be remembered that the species andesine has been formed for 

 the reception of those plagioclastic felspars in the volcanic rocks of the 

 Andes, which were termed oligoclase by the earlier observers. Some 



