1896. | NEW YORK ACADEMY OF SCIENCES. 249 
dark silicate is variable and frequently lacking. The orthoclase 
is almost invariably microperthitic. The rocks of this series 
contain the workable iron ores.” 
II. “A series of crystalline limestones and ophicalcites, black 
hornblende-pyroxenic schists and thinly laminated garnetifer- 
ous gneisses.” 
Ill. “A series of rocks of the gabbro family, ranging from 
pure aggregates of labradorite through varieties with increasing 
amounts of dark silicates to basic olivine gabbros. The rocks 
of this series contain the titaniferous iron ores.” 
IV. “A series of Palezeozoic sedimentary rocks, whose oldest 
member is the Potsdam sandstone and whose latest member 
thus far identified is the Utica slate.” 
V. “A subordinate series of igneous rocks that now form 
dikes, and one notable laccolite, and that are later than the 
Utica slate. These consist of ‘trachyte” (bostonite) and of 
basic dikes, mostly diabase.” 
PROPOSED CHANGE IN THE CLASSIFICATION. 
The contention of this paper is that there should be inserted 
between III. and IV. of the above classification a sub-division, 
as follows: 
A subordinate series of igneous rocks that now form dikes, 
that followed after the dynamic metamorphism of the first three 
series and antedated the beginning of deposition of series IV., 
and that in their typical development consist of diabase. 
And furthermore, that from the description of series V. the 
word diabase be stricken out, and that the last sentence of this 
description be made to read that these consist of “trachyte ” 
(bostonite), and of basic dikes, mostly camptonites and mon- 
chiquites. 
THe DIKEs. 
Description.—The various rock species which the dikes fur- 
nish have been recently so fully described by Kemp and Mar- 
sters* that any extended description of them here seems super- 
fluous. A group of acidic dikes of trachytic habit occurs to 
which the name bostonite has been applied. By far the greater 
number of the dikes are quite basic, and are called diabases, camp- 
tonites, monchiquites or fourchites, according to variations in 
mineral content and in structure. 
Distribution.—Perhaps the earliest impression to be gained 
concerning the distribution of the dikes is that they are found 
more frequently cutting the Pre-Cambrian series than the Pa- 
* Bull. U.S. Geol. Surv. 
TRANSACTIONS N, Y. ACAD. ScI., Vol. XV., Sig. 17, Sept. 25, 1896. 
