252 H. P. CUSHING—SYENITE-PORPHYRY DIKES. 
and decreasing silica into the latter. The following table permits of 
some interesting comparisons : 
I II III IV Wh VI. VII 
SiO Mcrae ee 63.02 64.63 60.03 59.70 54.61 52.53 50.36 
AE Oeics d clerteseteuectes 14.87 18.15 20.76 18.85 22.07 18.31 19.34 
BekOses aoe 6.53 3.05 4.01 4.85 2.33 0.24 6.94 
EOE. dereaiepacal lite BAU eale nae moos OND laste eres 2.50 6.43 \ 
WENO, ac roeateeeee. 0.46 NID (OO GF] ee he <a APR lf bags no ares OSL5 Fee 
CaO re Ree 1.12 1.54 2.62 1.34 2.51 3.15 3.43 
Nic @ ree roe ase 0.95 0.50. 0.80 0.68 0.88 1.82 | Undet. 
Ke OR cos ehtecrre 5.62 4.79 5.48 5.97 5.46 6.47 Toll 
Nar Oi Benita eas rans 5.80 5.80 5.96 6.29 7.58 7.26 7.64 
LENO Sarat ch arena ncaa coum de aollac an aan eabooees 0.15 TBO |e cee 
WOSSieee cn ieee 1.45 1.08 0.59 1.88 113 1.16 3.51 
99.87 | 100.54 | 101.07 99.56 99.31 99.83 98.80 
I. Dike 27, quoted from previous table. 
Il. Quartz-syenite from Fourche mountain, Arkansas, by J. F. Williams. <Ar- 
kansas Geological Survey, 1890, vol. ii, page 99. Analysis by R. N. Brackett. 
III. Pulaskite, Fourche mountain, Arkansas. Op. cit., page 39. Analysis by 
R. N. Brackett. ‘ ‘ 
IV. Elzeolite-syenite, Fourche mountain, Arkansas. Op. cit., page 81. Analysis 
by W. A. Noyes. 
V. Eleeolite-syenite, Caldas de Monchique, Portugal. Neues Jahrbuch fur Min- 
eralogie, Beilageband iii, 1885, page 271. Analysis by Kaleszinsky. 
VI. Dike 9, quoted from previous table. 
VII. Eleeolite-syenite, Beemerville, New Jersey, by Kemp. Transactions of the 
New York Academy of Sciences, vol. xi, page 67. Analysis by F. W. Love. 
The Arkansas quartz-syenite can in all probability be regarded as a 
differentiation product from the eleolite-syenitemagma. It differs from 
dike 27 (analyses I and II) mainly in its somewhat higher alumina. 
The pulaskite and eleolite-syenite (III and IV) are rather acid mem- 
bers of that group. Dike 32 of the Adirondack rocks has a silica per- 
centage of 59.20, and though it has not been fully analyzed would prob- 
ably yield results bearing the same relation to III and IV that I bears 
to II, namely, an equivalent silica percentage but lower alumina. A 
like result is obtained when VI is compared with V and VII, the former 
of which is regarded as a normal eleeolite-syenite, while the latter is 
rather basic, as noted by Kemp. In these nephelite has formed abun- 
dantly, whereas there is no trace of it in the Adirondack rocks, so far as 
the writer has been able to detect. An interesting parallel range is shown 
by the two series, one of which is normally more acidic than the other, 
the two throughout differing principally only in the silica-alumina ratio. 
