Editorial Comment. 319 
of the past twenty-five years would be found to hold, were the 
subject gone over again with the methods of research avail- 
able today. By some plasticity is looked upon as largely due 
to the chemical properties of the clay; and undoubtedly the 
amount of combined water has an important influence. With 
others the matters of size, shape, and relative abundance of 
the constituent particles and their conduct towards absorbed 
water are primary factors. It must, however, be evident to 
any one who peruses the literature at all carefully that there 
still remains much to be learned, and that much that is writ- 
ten consists in merely a reiteration of statements made many 
years ago. before the perfection of the microscope as an in- 
strument for the study of rocks, and while the science of 
chemistry was yet in its infancy. 
In spite of much good work that has recently been done, I 
can but think that the clays have not as yet received the atten- 
tion they deserve from a strictly scientific standpoint. They 
are complex bodies, with complex and striking peculiarities, 
and there is ample field for further investigation. 
The immediate cause of the above is the appearance in the 
Neues Jahrbuch fiir Alineralogie, Geologie und Palaeonto- 
logie, XV Beilage-Band, 2d Heft, of an article comprising 
pages 231-393, by H. Rosier, entitled Beifrage cur Kenntniss 
einiger Kaolinlagerstatten. The paper represents a large 
amount of work and is worthy of careful perusal and consid- 
eration, even though one should be inclined to question some 
of the conclusions. 
This writer reserves the name kaolin to the raw product 
obtained by washing the natural kaolinized granite or quartz 
porphyry. The apparent varying composition of kaolin, as 
shown by different analysts, he regards as due to admixed im- 
purities. The presence of a free aluminous hydroxide, as 
claimed by Kasai. and also the slight deficiency in silica com- 
monly shown, he looks upon as due to a lack of accuracy in 
analyses. 
He finds no sharp line of separation between kaolin and 
fireclays ; in this most writers will agree with him. The plas- 
ticity of kaolin and the fireclays he regards as due princi- 
pally to the flattened form of the constituents, their soft- 
ness, and their fineness. The hard-burning of many of the 
plastic clays he regards as due largely to the small size 
