T. S. Hunton Laurentian Rocks in Massachusetts. 77 
panying gneiss closely resemble the Laurentian rocks of other 
regions, and scapolite, apatite and serpentine occur as associ- 
ated minerals, though the latter was rare in the quarries then 
visited. A few days afterward Mr. Burbank kindly sent me 
Specimens of a mixture of limestone and yellowish-green ser- 
pentine from another quarry in the vicinity, which I had been 
unable to visit, and these have proved to be rich in Hozoon 
anadense, e continuous and complete calcareous skeleton 
of the fossil does not appear in these specimens, which seem 
ike some portions of the rock from Grenville, as described b 
Sir W. E. Logan, to be made up of fragments of the calcareous 
shell of Eozoon, mingled with grains of serpentine, and cemented 
by crystalline carbonate of lime. In the specimens from Gren- 
ville, and from most other localities, the mineral matter replacing 
the sarcode and filling up the canals and tubuli in the calea- 
reous Kozoon skeleton, is generally serpentine or some other 
silicate. Both Dawson and Carpenter however, it will be recol- 
lected, found that in the fragmentary Eozoon from Madoe, and 
im some small portions from Grenville, the injected mineral was 
like the shell itself, pure carbonate of lime, though readily dis- 
tinguishable by differences in texture and transparenc from 
the shell. Such is also the case with all the = sel es 
ese specimens from Chelmsford, it should be said, have 
been Spina) and satisfactorily identified by Dr. Dawson. 
The argument from ant mas § and lithological resemblances 
in favor of the Laurentian age of the limestone in question is 
therefore now supported by the undoubted presence in them of 
