18 R. Pumpelly— Pseudomorphs of Chlorite after 
imbedded on the surface planes, and in the interior - the crys- 
tals, both in the chlorite and in the unaltered garne 
I have made several thin sections passing p alex the mid- 
dle of crystals, about one inch in diameter, and have studied 
them underthe microscope, making such examination of the 
optical characteristics as the petupe cH the minerals and the 
limitations of the method would p 
nder a one-tenth inch eet (500 diameters) the garnet ap- 
pears not to be strictly homogeneous in texture ; “it has a 
eurdled structure, neg, of a transparent bluish-white fill- 
ing the irregular meshes of a less clear, white net-work. Bot 
of these portions of the garnet are isotrope, remaining dark 
through a aa revolution between crossed nicols. Throughout 
oth of t members are scattered exceedingly minute par- 
ticles of a ete red substance (hematite ) and larger 
opaque grains and discoidal plates. 
A glance at a section under a low power shows that the 
change has taken place by an attack on the garnet along the 
countless fissures that traverse it in every direction (fig. 1), 
progressing most rapidly in larger cracks, and ramifying 
through the more minute on 
Two substances, one sreenish yellow, the other clear green, 
seem at first sight to be among the products now forming the 
sie Soe though, as we shall - see, they both probably 
rae to the same mineral. 
he slightly greenish-yellow mineral (fig. 1) surcrounde the 
oe ee garnet mane nts in bands which are in places clear 
and transparent, and in others are marked with longitudinal 
wavy lines, which Seekauls indicate the cleavage of the mineral. 
From these broader bands, narrow ones branch off to form an 
intricate net-work in the garnet fragments. The same mineral 
occurs in isolated and grouped, long and slender crystals, which 
often branch out from or intersect the b ands; while in other 
places the bands are often made up of these ervstals, arrang 
more or less parallel to each other. 
These bands are generally ;,,;.to ;4, of an inch wide, and 
under a low power (figs. 1 and 2) — edges are sharply defined. 
Where a garnet fragment has been entirely destroyed, its place 
is occupied by an interwoven mass of them, often associated 
with irregular patches of the green substance described below. 
Mader a high power, both the transparent red particles and the 
ue grains and plates that were noticed in the garnet, are 
ed in this aligmon-prodicts . 
degree 
and an tn app prcshle amount for color, changing from “very 
antl (wit he 
