3881.] 
279 
[Crosby. 
General Meeting. November 2, 1881. 
The President, Mr. S. H. Scudder, in the chair. Twenty- 
three persons present. 
The President announced in fitting words the death of Mr. 
John Amory Lowell, a Patron, and for many years an officer, of 
the Society, and the giver of the “ Lowell Herbarium.” 
The following papers were read : 
ON THE CLASSIFICATION OF THE TEXTURES AND STRUC- 
TURES OF ROCKS. 
BY W. O. CROSBY. 
PART I. TEXTURES OF ROCKS. 
The study of rocks, from a purely lithological standpoint, pre- 
sents four different aspects. We may investigate: first, the 
chemical composition ; second, the mineralogical composition ; 
third, the microscopic structure ; and, fourth, the texture . 1 And it 
is now generally conceded that the accurate description and 
proper classification of almost any rock demands a knowledge of 
it in these four different phases. But accurate and especially intelli- 
gible description demands, in addition to fullness of knowledge, an 
equally comprehensive and definite nomenclature. Every one 
knows what Botany has gained from the possession of such a 
precise descriptive terminology, which makes every description 
equal to a picture. 
Chemistry has long been favored with an approximately ade- 
quate nomenclature, the good influence of which has been felt in 
every field in which the chemist has labored. Rocks and their 
constituent minerals were among the first bodies investigated by 
chemists, and a vast multitude of analyses has been made. So 
that our knowledge of the chemical composition of rocks appears 
1 The specific gravity, hardness and color, depending so largely upon the composition, 
and being usually known when that is known, need not be enumerated here. 
