BULLETIN OF THE BUSSEY INSTITUTION, 9 
This rock appears to consist of a syenitic base through 
which crystals of orthoclase are scattered . . . . . 5.568 0.037 
Compact, fine-grained gray rock (?a somewhat aigered 
diorite) from ‘‘red-gravel locality ’’ on Clyde Street, 
Brookline, Mass. .. . . 0.997 0.121 
Dark-colored, compact, fine- ereinad debris (2) fron Bos: 
ton and Providence turnpike, West Dedham, Mass.. . 1.007 0.194 
Similar to the preceding, from Chelsea Street, Everett, 
Mass., as above described . . .. . . - 0.684 0.846 
Dark fae. -grained diorite, similar to the neue! but 
carrying numberless minute specks of iron pyrites, from 
City Ledge, Somerville, Mass.. . . . 0.303 0.444 
Rock, formerly called Syenite, from the Milk ow mine | 
(Dane’s Ledge), Somerville, Mass., well known to 
mineralogists as a locality for phrenite and other 
minerals. From the analyses given below, it would 
seem as if this rock might fairly be classed as a diorite, 
though it differs Very materially in texture and appear- 
ance from the diorites ordinarily found in the vicinity 
of Boston. ‘The crystals of the minerals which compose 
the Milk Row Rock, unlike those of the common diorites 
of the region, are as large and coarse as those in the 
syenites ordinarily used for buildings; and the rock 
itself, though massive, compact, and tolerably hard, 
as it exists in the solid ledge, disintegrates rapidly 
when exposed to the weather, and falls to a fine red 
gravel, that is much esteemed for spreading upon garden 
walks: — 
I. A sample of the original undecomposed, or only 
slightly decomposed, dark-colored rock * from Dane’s 
Sa ay WE as ap ape fe. ay L404: 0.580 
* On further examination, it appeared that this particular specimen of the 
rock, dried at 110° C. contained per cent of: — 
Alumina 
Silica. and Lime. Magnesia. 
Ferric Oxide. 
49.82 $1.82 8.42 8.03 
I find furthermore in one of my old note-books, for the winter of 1851-52, 
partial analyses of three samples of rock from the Milk Row quarry, to the 
following effect : — 
Loss on Ferrous Sulp. 
ignition. Silica. Alumina. oxide. Lime. acid. 
Ist sample. . . 5.05% 46.18 15.62 23.93 6.51 0.45 
ee sh 40.45 18.50 16.40 ees 0.21 
ed ‘i Tie O00 88.58 19.46 a —— —_— 
With regard to these figures it should be said that the “loss by ignition” 
does not truly represent the amount of water in the rock, since some of the 
ferrous oxide that is contained in it takes on oxygen during the ignition. 
