1881 .] 
285 
[Crosby. 
mode of arrangement of the constituent particles. This texture 
occurs commonly in association with the crystalline, compact 
and vitreous, but rarely with the fragmental. 
The concretionary texture, again, is clearly determined, not by 
the form or size, but by the mode of arrangement of the constit- 
uent particles, for the concretions are not single particles but 
aggregates of particles. This texture is of common occurrence 
in connection with the fragmental and compact textures ; and the 
nodules of mica in the granite of Craftsbury, Vermont, to men- 
tion only a single illustration, shows that it may occur with the 
crystalline texture ; while perlite is a notable instance of its asso- 
ciation with the vitreous texture. 
The vesicular texture, except in the comparatively unimpor- 
tant cases where cavities have been produced through the solu- 
tion of fossils or crystals, is limited to volcanic rocks ; and hence 
is rarely found except in association with either the compact or 
vitreous textures. This is, however, commonly regarded as a 
simple texture ; and to the minds of many geologists, no doubt, 
the proposition is absurd that a rock can be at the same time 
compact and vesicular. I venture to maintain, nevertheless, that 
this necessarily follows from a proper definition of the two terms. 
Few would deny that pumice is a vesicular vitreous rock, yet 
ordinary lava is just as truly vesicular compact. The amygda- 
loidal texture, by virtue of the definition, is necessarily limited 
to the same classes of rocks, and to the same primary textures, as 
the vesicular texture. The tufaceous texture is something quite 
distinct from the vesicular ; and it can scarcely be said to occur, 
except with the compact texture. 
All the secondary textures enumerated so far are determined 
by the mode, i. e., the pattern, of the arrangement of the con- 
stituent particles ; and other, but less important, varieties falling 
under the same general definition, as fibrous , columnar , shelly , 
etc., might be added to the list. I notice next, however, two tex- 
tures depending on the strength of the union of the particles. 
These may be called the firm or strong and the friable or 
earthy . They occur with pretty much all the primary textures. 
Friable and earthy are not strictly synonymous, but the former 
may be properly restricted to fragmental and crystalline rocks, 
