244 Prof. T. G. Bonney. Notes on the [Jan. 31, 



bears, under the microscope, a general resemblance to that from 

 La GJ-uardette, Cantal, figured by MM. Fouque and Levy, Roches 

 Eruptives, PI. xxix. 



Two other specimens, labelled respectively "Puerto, de Tanguieta 

 Encillada para Nina-urcu " and " Machai Grande, subida at fichaco de 

 Puguampa, lado norte," exhibit only varietal differences, so that it is 

 needless to enter into the details of their microscopic structure. The 

 fourth specimen, labelled Tioloma grande jpaso a vintnnillas, is a rock of 

 similar character to the other, but it incloses an oval mass of darker 

 colour and more granulated structure, which has a fairly sharp 

 boundary, so that it somewhat resembles an inclosed pebble. The 

 latter is composed of a clear mineral, generally polygonal (approxi- 

 mately hexagonal) in outline, containing some minute microlithic 

 inclosures. This mineral gives occasional indications of zonal banding 

 and oscillatory twinning ; if a felspar it is difficult to assign the species ; 

 there is also a fair amount of a pale augite (which has subsequently 

 consolidated), and of an iron peroxide in irregular granules, and as a 

 staining in what appears to be the sparse remnant of a glassy base, 

 which gives a faint indication of a fluidal structure. I am disposed 

 to regard the mass as a node rather than an included fragment, 

 caught up by the melted lava. 



The next group of nine specimens all bear the label Grater of 

 Guagua-Pichincha, the more precise localities being (I translate 

 the Spanish terms) (a) Ascent of the Grater, N.W. slopes ; (6) Idem; 

 (c) Idem; (d) Edge of Grater, N.W. side; (e) Idem, N.E. side; 

 (/) Commencement of the Descent of the Grater, 8.E. side; 

 (9) Slopes of the Crater, N.E. side; (Ji) Bottom of the Crater, near the 

 ancient fumaroles (a very decomposed specimen) ; (1) Bottom of the 

 Crater, brink of the inferior Crater. These specimens all bear a 

 general resemblance to one another, and, as most of them are not 

 very well preserved, I have had only two of them cut for microscopic 

 examination, as I felt certain that the differences which the others 

 mio-ht present would be only varietal, and that it was doubtful 

 whether some would be in a fit state for examination. These are the 

 specimens marked (a) the best preserved of the series, and (e) that 

 from the summit rim of the crater, which may be regarded as about 

 in an average state of preservation. 



The former of these specimens (a) has a compact pale-grey matrix, 

 in which are scattered little crystals of whitish felspar and rather 

 elongated prisms of a mineral resembling a black hornblende, which 

 do not exceed about 0*2 inch in length, and are often less. 



In the first stage of consolidation are : (1) Crystals of felspar, 

 with regular outlines, probably in most instances labradorite ; 

 they generally contain, though in variable quantities, microlithic 

 inclosures. These sometimes have a rough zonally banded arrange- 



