Crosby.] 
284 
[November 2, 
But, in addition to at least one of the primary textures, a rock 
may or may not possess one or more of what may be called sec- 
ondary textures. These are determined by the way in which the 
particles are united, the mode or pattern of the arrangement, etc. 
The number of secondary textures is rather indefinite ; but those 
named in the table are sufficient to illustrate the classification, 
the most vital and most original feature of which is the recogni- 
tion of the fact that there is an essential difference, in their rela- 
tions to the rocks, between the primary and secondary textures ; 
one of the former being necessarily present in every rock, while 
one or more of the latter may or may not occur along with the 
primary texture. 
In some rocks, several secondary textures occur combined with 
one primary texture ; as in laminated and porphyritic gneiss, the 
primary texture here being the crystalline ; or as in laminated 
and concretionary compact limestone. The table, however, for 
simplicity’s sake, is constructed to show only the possible combi- 
nations of one secondary with a primary texture. Undoubtedly 
the most important of the secondary textures is the laminated. 
This exists where the constituent particles, whatever their form 
or size, are arranged in more or less regular and parallel bands or 
layers. We may distinguish two principal kinds of laminated 
texture, according as the lamination is or is not accompanied by 
easy splitting or cleavage. Banded appears to be a suitable name 
for the texture in the absence of easy splitting. But, where easy 
splitting exists, lithologists have found it convenient to distin- 
guish between the easy splitting or lamination cleavage of crystal- 
line rocks on the one hand and of the fragmental and compact 
rocks on the other ; the term schistose being applied and restricted 
to the former, and the term shaly to the latter. We may also 
properly distinguish between both these and the easy splitting 
that is independent of and usually at variance with the layers 
varying in composition, color or texture, i. e., slaty cleavage or 
cleavage properly so-called. 
In all cases of the porphyritic texture, the primary texture is, 
in part at least, crystalline, and it may be wholly so. Neverthe- 
less, crystals alone do not make the porphyritic texture, but that, 
as with all secondary textures, depends very largely upon the 
