K<ii tori a! Comment. 109 
ing where and what buildings have been erected of the various 
granites exhibited, a feature which was not seen on any other 
similar exhibit. The most interesting portion of the Massa- 
chusetts exhibit was in the gallery of the Mines and Mining 
building. It was collected by Dr. W. H. Hobbs, 0. L. Whittle 
and Geo. E. Ladd, and displayed many interesting rock struc- 
tures as well as a large number of minerals. There were many 
fine samples of margarite, with its divergent cleavage plates, 
of steatite, with its wavy or step-ladder structure. Margarite, 
chloritoid and emery were from Chester, the steatite from 
Bland ford. 
A polished slab of mica schist, from Great Barrington, 
loaned by Dr. Hobbs, illustrated the formation of a secondary 
"banding" transverse to the sedimentary structure. This, 
however, is hardly a banding, but a schistosity, although it 
has been mistaken for a sedimentary structure by several 
geologists. This is the same slab as that used to illustrate 
Dr. Hobbs' paper on this subject in the Bulletin of the Geo- 
logical Society of America (vol. iii, p. 460). A mica schist con- 
glomerate, from near the base of the Taconic, from the Hoosac 
tunnel, contained pebbles of granite and gneiss, and illustra- 
ted the manner in which the old fragmentals approximate the 
petrographic characters of a true crystalline rock. There was 
also a very nice polished slab of lilac and iridescent scapolite 
from Bolton. This is associated in a limestone with a variety 
of minerals, such as diopside, beryl, nuttallite, etc. By Dr. 
Wolff the conglomerate has been found to pass into gneiss, 
the pebbles having a micaceous matrix. 
A building stone that has acquired some notoriety was ex- 
hibited from Somerville. This is a decomposing diabase. 
Prof. N. S. Shaler protested against its going into "memorial 
hall, 1 ' Cambridge, and prevented it. The owners, who lost the 
contract, brought suit against him for "defamation of prop- 
erty," but as there was no difficulty in proving that the rock 
is subject to rapid disintegration and has decayed to the 
depth of twenty feet along the joint planes, they recovered 
no damages. This stone has. however, lately been used in the 
foundations of Hastings hall. This collection demonstrated 
the superior qualifications of practical geologists in getting 
together such exhibits. It was not wholly "industrial," but 
