DESCRIPTION OF ILLUSTRATIONS. 147 



Fig. (i. Slide 194'"-". Pseu(loinor])h of clilorito after horiihlende. Gramilar epidote 

 iis developing from live di.stiiiet centers in the chlorite. The cldorite close 

 to the lett-baud ujjper edge of tlie crystal is composed of libers iter|)eu- 

 dicular to the crystal face, and appears to resist the encroachment of epi- 

 dote. The rock is a porjjhyritic diorite from the McKibben Tunnel. Mag- 

 nified 48 diameters. 



Fig. 7. Slide 194^-'^. A group of three hornblendes has been completely converted 

 into chlorite, and in these i)seiuIomorphs epidote has develoi)ed from the 

 centers in gXiinular masses and fagot-like bundles. The growth of epi- 

 dote needles into the chlorite (which is shaded a flat gray) can be excel- 

 lently observed at the right-hand edge of the cut, and between the left- 

 band and the middle crystals. In the left-hand crystal there are two 

 small patches of secondary quartz. The rock is porphyritic diorite from 

 the McKibben Tunnel. Magnified 40 diameters. 



Fig. s. Slide iSy'"-^". Pseudomorph of chlorite and epidote, after mica. The conver- 

 sion to chlorite probably proceeded from the cleavages, and the conversion 

 of chlorite to epidote has begun upon the same lines. The chlcnite as 

 usual is indicated by a flat gray tint. ]\Iinute denticles of epidote can 

 readily be seen under high powers, piercing the fibrous chlorite mass. 

 The rock is diorite-porphyry from the head of Ophir Ravine. Magnified 

 .30 diameters. 



Pig. it. Slide IOO^-m, Pseudomorph of epidote after hornblende. The epidote appears 

 to have crystallized from three different centers, and the radial needles 

 strike entirely across the crystal. The rock is a i)orphyritic diorite from the 

 McKibben Tunnel, part of the same mass the pseudomorphic phenomena of 

 which are illustrated in Figs. 6 and 7, and distant only eight feet from it. 

 It is the last stage of the conversion shown in Fig. 7. Slide 100 also 

 shows epidote developing in chlorite patches. Magnified 50 diameters. 



Fig. 10. Slide 197'^'^'. Pseudomorph of chlorite and quartz after hornblende. The 

 quartz occupies the central portion of the crystal, and seems to have been 

 deposited by substitution for chlorite. The chlorite border is fibrous, 

 excessively fine, and, as usual where this structure occurs, transmits 

 scarcely a ray of light between crossed Nicols. The approximate uniform- 

 ity of the chlorite zone suggests that the resistance ofl'ered by it to decom- 

 position has exceeded that of the chlorite for which quartz has been substi- 

 tuted. The very dark spots in the quartz are limonite, and there are two 

 small granular bunches of epidote in the chlorite, at the lower left-hand 

 corner of the cut. The slide is irom the same specimen as Fig. 9. Mag- 

 nified 100 diameters. 



Fig. 11. Slide 295'°''''. Colorless hornblende passing into a green variety of the same 

 mineral seen in cross-section. A large hornblende appears to have been 

 divided into cleavage prisms by chloritic decom])osition, much as in Fig. 2, 

 but with the additional dcveloiiment of the clinopinacoidal cleavage. 



