Crosby.] 
280 
[November 2, 
now to be tolerably complete ; and what is needed in the future 
is, not more analyses, so much as the generalization of results 
already reached, and the investigation of the origin, decay, meta- 
morphism and transmutation of species. 
Our knowledge of the mineralogical composition of rocks has 
made a great advance since the time when basalt was regarded 
as a simple mineral ; and the first application of the microscope 
to the study of rocks marks an epoch in the history of this phase 
of Lithology. Since that date, our notions concerning the com- 
position and limitations of species have become vastly more defi- 
nite ; and there has been a corresponding improvement in the 
nomenclature, as shown by the advent of the adjective terms — 
essential , accessory , original , secondary, felsitic, amorphous , etc. 
The microscope has also revealed a whole world of structure 
whose existence was scarcely suspected before, thus creating a 
new department of the science. 
Not one of the four general characteristics of rocks which we 
have enumerated presents fewer dificulties to the investigator 
than texture. It is the most superficial feature and demands only 
the simplest kind of macroscopic observation. It is to Lithology 
very much what morphology is to Botany, but with this important 
difference : the descriptive nomenclature of morphological Botany 
is one of the most perfect in the whole range of natural science, 
while that of the textures of rocks is very far from being satis- 
factory. The vocabulary of this subject is not especially deficient 
in terms, but many of them have been so variously defined by 
authors as to have practically lost their significance. 
In the opinion of the writer, the greatest obstacle to progress 
in this direction is the absence of a proper classification of 
textures. Not only do authors differ widely in their definitions 
of particular kinds of texture, but it is difficult to find two works 
containing systematic descriptions of textures in which they are 
taken up in the same order. The arrangements are purely hap- 
hazard ; and, so far as I can learn, it has occurred to no previous 
writer that there is any best order, that there may be, in short, a 
natural classification of textures. 
It is my present purpose, however, to show that there are cer- 
tain natural and necessary relations existing between the different 
