No. 9.— Contributions from the Petrographical Laboratory of the 
Harvard University Museum. 
TL. 
On Keratophyre from Marblehead Neck, Massachusetts. 
By Joun H. Sears. 
Tus interesting rock formation was first noticed by Prof. W. O. 
Crosby in the American Naturalist (Vol. XI. No. 10, 1877, p. 585), 
where he says: ‘‘ Near the middle of the southwest side of the harbor, 
visible only at low tide, is a hard, whitish, fine-grained sandstone or 
arenaceous slate. It overlies unconformably the banded petrosilex 
found on the shore.” In the “ Occasional Papers of the Boston Society 
of Natural History, III. Contributions to the Geology of Eastern Massa- 
chusetts,” Professor Crosby says again of Marblehead Neck (p. 263) : 
“ Tt is not generally known that this rocky peninsula, which may be re- 
garded as lying on the extreme outskirts of the Boston Basin, includes 
beds probably referable to the same horizon as the slate and conglomer- 
ate on the south and west. Briefly stated the facts are as follows: 
Near the middle of the northwest shore of the Neck, visible only at low 
tide, is a hard, whitish, fine-grained sandstone or arenaceous slate ; it is 
evidently largely feldspathic and turns yellowish on weathering. Por- 
phyritically interspersed through the rock are clear, almost transparent, 
rhomboidal crystals, from one eighth to one fourth of an inch long ; 
these have been examined by Miss Hattie A. Walker and proved to be 
orthoclase.” 
The next notice of this rock is in the Proceedings of the Boston 
Society of Natural History (Vol. XXI. Part 3, p. 288), “On the Tra- 
chyte of Marblehead Neck,” by Dr. M. E. Wadsworth, in which he 
says, “ Near Boden’s Point, on the northwest shore of Marblehead 
Neck, there is to be seen, exposed between high and low tide, the re- 
mains of a trachytic overflow.” On page 290, Dr. Wadsworth says: 
“One of the feldspars, porphyritically enclosed in the groundmass, was 
obtained in the section. This is clear, glassy, and contains only a slight 
VOL. XVI. —NO. 9. 
