reverse succession. The succession here noted is also in accord with artificial experiment.

Between the general diorite that forms the greater part of the Rosetown area and the diorites and mica-diorites of the main area, the writer can trace no mineralogical differences worthy of note except those already given. Omitting the hy persthene and olivine from consideration it would doubtless be possible to find types corresponding with those described by Dr. Williams, but it would simplify matters in no respect. The writer would express his obligations to Dr. Williams for the kind loan of a series of typical sections from the main Cortlandt with which to compare his results. As mineralogical aggregates they are quite analogous.

Around the edges of the area, where the massive rocks come in contact with the gneiss, numerous small dikes have been developed. They vary from one to several inches in width and consist very uniformly of brown and green hornblende, 0-1mm to 0.3mm intermingled with feldspar masses no larger. The hornblende crystals tend to have their longer axes arranged parallel with the walls of the dike. The feldspar

rarely shows twinning and its composition must generally be inferred from the analysis. The feldspar is however filled with inclusions of hornblende, rutile, and less often apatite. The following analysis (spec. 66a) kindly made by Mr. L. M. Dennis, shows the notably high percentage of TiO,, which

would be inferred from the slide.

The structure of most of these dikes is quite uniformly allotriomorphic and in the majority of cases no amorphous matter or distinct magma can be noted (exception mentioned later). The hornblende has generally crystallized first after the oxides but at least one instance (slide 68) has been remarked in which a plagioclase is included in hornblende. Along the border of one small offshoot (66a) which is 4mm broad the microscope shows a selvage of fine quartz and feld

*All of the iron estimated as FeO.

spar crystals 0.1mm to 0.3mm, evidently produced from the large quartz and feldspar of the gneiss by contact. In polarized light this resembles a beautiful fine mosaic (kataklasstructur ?) apparently protecting the gneiss from the further metamorphosing action of the dike. These contact phenomena are to be seen very generally around the area but the best exposure is perhaps in the roadside in D, 5 and C, 6. On the roadside in A,6 where the area trends to the north at the site of a supposed silver mine is a dike which proves to be a hornblende porphyrite which is interesting as exhibiting a different facies from the other contact dikes, and one more of the character that would on a priori grounds be expected. It seems reasonable to infer that this latter was intruded between walls possessing less heat for some reason than those of the former, and was thus more suddenly chilled.

From somewhere near this same locality a piece of so-called iron ore was given me by a farmer, but the exact point was kept secret. It appears on section to be a hard and very compact mixture of magnetite and emery or corundum and to be thus a similar occurrence to those in the main Cortlandt.*

In the bed of the brook below the M. E. parsonage (B, 8) is another most peculiar contact mass. The rock is of porphyritic character very similar to the curious porphyritic rocks occurring near Montrose. It contains, however, all manner of included masses of gneiss and limestone, resembling a pudding into which the enclosed masses have been stirred. In macroscopic characters the enclosed limestone resembles very closely the mass on the summit of Stony Pt. Under the microscope it is seen to be an exceedingly finely crystalline aggregate of calcite crystals1mm in diameter mingled with some, more brightly polarizing but undetermined mineral in crystals no larger. Scattered grains of pyrite are also to be seen.

Back of the lime-kiln in B, 8 and 9 is found the mass of included marble above referred to. This is colored dead black on the map. As much as thirty feet in thickness have been exposed by the quarrying, but the exact contact with the diorites is not shown. They however are found but a short distance north and south, proving it to be an included mass. In general the limestone is a beautiful white crystalline marble, in places very curiously banded. There are, however, numerous masses along its outer edges which are shown by the sections to consist quite entirely of tremolite. The limestone also exhibits the half fused appearance of similar contact masses the world over. A similar limestone or marble is said by the farmers to have been found in the bed of the brook near the porphyritic * J. D. Dana. This Jour., III, xx, p. 199--200.—G. H. Williams, ibid., xxxiii, p. 194.

rock above referred to, but I was unable to find it myself. If so, it probably furnished the included masses there mentioned.

Along the roadside in B and C, 5, a mass of included gneiss is to be seen. This is very firmly crystalline, appearing almost massive in character, and is more compact and hard than the neighboring gneiss in place. It is said that stone for bridgepiers and culverts was obtained here by the West Shore Railway engineers on account of its strength.

While this area is far smaller than the original Cortlandt, it yet is large enough to exhibit in its mass very perfectly the coarse, holocrystalline structure, characteristic of plutonic masses, shading off toward the contact into finely crystalline or porphyritic types. Moreover, as the general axes of both this area and the main Cortlandt run approximately parallel to the strike of the gneiss and limestone the inference is suggested that they welled forth from longitudinal fissures produced by the general folding. Also that the Rosetown mass broke across and through the intervening beds of limestone and gneiss and formed the westerly extension and that in its passage it took up the masses of limestone and gneiss now found included. From the undisturbed condition and unconformable strike of the neighboring Triassic beds it is safe to infer that the outbreak was previous to the Trias. It is clearly subsequent to the Tompkins Cove limestone. If this is Cambrian as seems increasingly probable the intrusion of the Cortlandt series certainly occurred in the Paleozoic.* We would infer, however, from its general holocrystalline character that the mass, as now seen, solidified a considerable distance beneath the surface and under great pressure and slow cooling.

The credit of the discovery of this area belongs to Dr. N. L. Britton, and the writer is indebted to him for the suggestion of its elaboration. It is not improbable that other outlying masses may be found in further field work in the Highlands. In the rear of the Tompkins Cove School numerous stray pieces of feldspar porphyry, like the rock near Montrose Station have been found by the writer quite disconnected with either area. In the foot of the Dunderberg the West Shore R. R. cuts show numerous dikes which seem to be closely related. From this same region Mathert mentions under the name greenstone not a few localities of probably intrusive rock, but his descriptions are too unsystematic to serve as other than suggestions for subsequent workers.

Geological Laboratory, Cornell University, Ithaca, N. Y.

*J. D. Dana. This Jour., III, vol. xxviii, p. 386.

+N. Y. State Survey, Geol., 1st Dist., p. 539 and elsewhere.

ART. XXVI.—The Contact-Metamorphism produced in the adjoining Mica schists and Limestones by the Massive Rocks of the "Cortlandt Series," near Peekskill, N. Y.; by GEORGE H. WILLIAMS. With Plate VI.

IN three former papers I have described the principal types and some of the intermediate varieties forming the complicated group of massive rocks known as the "Cortlandt Series."* Aside from their own intrinsic interest, these rocks are hardly less worthy of attention on account of the unusual contactmetamorphism which they have occasioned in the adjoining schists.

The area occupied by the Cortlandt massive rocks—about twenty-five square miles in extent-is bordered on the south mainly by mica schists and on the west mainly by limestones. Both of these rocks have been altered by the masses which have broken through them, although the metamorphosing influence has not extended far from the contact. The gneisses, on the other hand, which border the Cortlandt area on the north, do not appear to have been materially affected.

The two localities where these phases of metamorphism were best observed--both already known through Professor Dana's descriptions of them—are here selected as typical. A further search would doubtless reveal other localities as interesting, while the emery and iron (pleonaste) deposits already described by the writer as occurring in the southern part of the Cortlandt area,† may with certainty be referred to the same category. The two typical localities referred to are: for mica schist metamorphism, Cruger's Station; for limestone metamorphism, southern end of Verplanck Point.

I. Contact-metamorphism in the Mica Schist.

If we leave the train at Cruger's, a station on the Hudson River Railroad about four miles south of Peekskill, we find ourselves near the river-bank which at this point extends nearly west for about three fourths of a mile. Near the shore the rocks exposed are mica schists, but these are frequently covered by beds of clay which is used in the numerous brick-sheds of this region. Not over a few hundred yards from the shore rises a rocky wall which extends nearly parallel to the river bank until this bends toward the north. This wall coincides with the southern edge of the massive rocks of the "Cortlandt * This Journal, III, xxxi, p. 26, Jan., 1886; ib., xxxiii, pp. 135 and 191, Feb. and March, 1887; ib., xxxv, p. 438, June, 1888.

+ This Journal, III, xxxiii, p. 194, March, 1887.

Series," which here consist of mica-diorite or mica-hornblendediorite. No exposure could display more favorably than this one the contact-phenomena between the massive rock and adjacent schists.

This small area is represented on Professor Dana's map,* but it is here reproduced on a much larger scale from the manuscript chart in the office of the U. S. Coast and Geodetic Survey in Washington. The particular points designated by let

ters are the same as those used by Professor Dana.* They represent three different sections across the schists, one 300--400 yards (lm); one 700 yards (o-p); and are 900 yards (9-8) west of Cruger's Station, and are as good as any that could be selected.

The mica schists of this area adjoin conformably the small limestone area at Cruger's Station and have an average strike N. 70° E. and dip 75° N.; i. e. they strike nearly parallel to the river bank and dip toward the massive rocks. On the shore they are highly crystalline, but not much crumpled or metamorphosed. As we follow them, however, across the strike they become more and more puckered and filled with lenses or eyes of quartz containing garnet and other contact minerals. In the schists themselves are developed staurolite, sillimanite, cyanite and garnet. The intensity of the metamorphic changes is directly proportional to the nearness of the * This Journal, III, xx, p. 195, Sept., 1880.