The metamorphism of the Paleozoic sediments is intense. The Lower Cambrian sediments, originally feldspathic muds, have been transformed into lustrous muscovite schists, microcline gneisses, and quartzites. The schists are closely crumpled, and show segregation lenses of quartz, holding needles of tourmaline. The Cambro-Ordovician limestone has become a white or mottled marble holding mica and tremolite. Quartzitic bands in places include needles of tourmaline. The Berkshire schist in the eastern outcrops shows coarse crystallization and the development of garnet and staurolite. In the axis of the synclinorium, however, the metamorphism of this rock dies out rapidly, and it turns to a grayish or greenish sericite schist. In New York State it passes gradually into the dark Hudson River slates.

It would seem that here the severity of the deformation is roughly in accord with the degree of metamorphism and is a sufficient explanation of the facts without invoking the aid of magmatic heat or emanations. Closer observation shows, however, a lack of exact accord between the local degree of deformation and the local degree of crystallization. The small synclines of Berkshire schist in the middle of the limestone valley show strong metamorphism even where not intensely deformed. The pinched axis of the syncline, although of the same stratigraphic level, shows a lesser degree of metamorphism. The limestone beds, even where flat-lying and showing the bedding fairly undisturbed, are nevertheless transformed into coarse marbles. The rocks of the valley have, however, been deeply buried beneath overthrust masses so that the greater depth at which they were deformed must have been a contributory factor in the metamorphism.

Turning to another side of the problem, what is the evidence or lack of evidence that batholithic intrusions

may lie below? The nearest Paleozoic granites, as mapped by Hobbs, lie on the axis of the anticlinorium some twelve miles south of the Connecticut-Massachusetts line. None are known in the synclinorium. Direct evidence is therefore lacking. The indirect evidence is as follows: The Lower Cambrian Dalton schists overlie the Archean complex and outcrop in anticlines within the limestone valley. They vary from muscovite schists to

W. II. Hobbs, in Preliminary geological map of Connecticut, by H. E. Gregory and II. H. Robinson, Conn. Geol. Nat. Hist. Survey, Bull. 7, 1906.

feldspathic quartzites. The schists show many segregation seams and lenses of quartz and feldspar, the quartz holding needles of tourmaline. The boron and fluorine which enter into tourmaline are elements not found in clastic sediments. They are commonly regarded as the evidences of pneumatolysis, but if so, they have the capacity to rise for great distances through metamorphic zones before entering into crystallization as tourmaline. It is well known that tourmaline tends to crystallize, especially in siliceous formations. Apparently, then, the volatile constituents have come as gases from some depth beneath in the Archean complex. That the boron and fluorine have shown a capacity to rise is most clearly shown in a quartzite member within the Stockbridge marble. At Ashley Falls, Massachusetts, the joints in this member show the development of tourmaline crystals in their walls, arranged across the bedding planes. The tourmaline is a replacement mineral lining the crosscutting joints and developed at the expense of preexisting biotite. In the Dalton schist, the development along the foliation planes conceals this kind of evidence of introduction, but the pegmatitic character of the lenses gives support to such a view.

Of course it is possible to discount the value of this evidence based upon tourmaline, and to cite the existence of fluorite deposits in regions free from any signs of igneous activity. But it is thought that the evidence given in the first part of this article on the widespread nature of subjacent igneous bodies, tends to support the view that where tourmaline is abundantly present, magmatic emanations were passing through at the time of its formation and supplied the volatile elements necessary for its development.

Another line of evidence is found in extensive infiltrations of silica which have developed, in the Stockbridge marble, reefs of malacolite, tremolite, and quartz, over a distance of eight miles between Falls Village, Connecticut, and Sheffield, Massachusetts. Several varieties and stages of the action may be noted. Reefs of rugged rocks show that, first, an infiltration of siliceous waters deposited quartz in veins. Then an increase in temperature occurred, the waters attacked the lime and magnesia, and coarse-grained tremolite replacements occurred. The reaction did not occur wholly in place, however, since the materials were taken into solution and deposited in veins AM. JOUR. SCI.-FIFTH SERIES, VOL. I, No. 1.-JANUARY, 1921.

showing all gradations from quartz to pure tremolite. The tremolite veins in places cut the older vein quartz and give clear evidence of the carrying of tremolite in solution.

Between Ashley Falls and Falls Village another phase may be seen. Tough, massive reefs of white pyroxene rock, malacolite, are found, with granitic grain and in some places clearly developed by infiltration, not by the mere alteration of an impure marble. The reefs occur in certain local areas and are not restricted to a definite horizon in the marble. The large size and unbroken character of the crystals, as well as the presence of pyroxene rather than amphibole, ally these occurrences with the phenomena of igneous contact action, and show a development after the regional mashing. In general, these reefs are surprisingly free from the minerals usually associated with igneous emanations. Only rarely is pyrite or chalcopyrite found, and in only one locality near the eastern margin of the limestone is tourmaline associated. Here, near the head of Whiting River, large crystals of feldspar and phlogopite and smaller ones of tourmaline occur with malacolite. Thus this evidence, while indicative of rising waters, does not clearly show those waters to have been magmatic.

LACK OF METAMORPHISM IN THE PENNSYLVANIA FOLDS. The valley in Pennsylvania between the pre-Cambrian and Silurian outcrops corresponds in structural position to the valley in western New England which has just been described. It is a region of close folding, the folds becoming open farther west in the state. The limestones of this eastern belt have been crumpled into folds, many of which are but some tens of feet in radius. In other places, extensive overturning into recumbent folds has taken place. The argillites above have been mashed into slates holding much of commercial quality. The writer has recently assembled the evidence to show that a great depth of cover has been removed from this region,10 but the nature of the structures alone serves to make it clear that they originated at considerable depth. It is regarded as a tract of great crustal shortening,11 and the

10 Joseph Barrell, The Upper Devonian delta of the Appalachian geosyncline, this Journal (4), 36, 429-472, 1913; 37, 87-109, 225-253, 1914. "R. T. Chamberlin, Jour. Geology, 18, 228-251, 1910.

depth at which took place the folding of the rocks now exposed was certainly in places several miles, even allowing for erosion accompanying folding. Chamberlin's restoration, not allowing for erosion, shows a depth of four and a half miles as a maximum on the west, and six miles as a maximum on the east. In depth of burial and intensity of deformation, this region must therefore be regarded as having been subjected to conditions as severe as those of western New England. No evidences of Paleozoic igneous intrusion younger than the Cambrian are found in the region, the nearest of such intrusions being some pegmatite dikes in the Philadelphia region.

What, then, is the degree of regional metamorphism as compared to western New England? It is found in answer to be insignificant. The effects have been a reduction of porosity and a partial elimination of the combined water from the argillaceous sediments. At the base are limited thicknesses of Lower Cambrian quartzite with some beds of hydromica slate. Above this, the Cambro-Ordovician limestone shows no degree of alteration. The upper Ordovician slates are dark and rather dull in luster. Under the microscope they show a grain beneath a tenth of a millimeter in diameter. Sericite giving aggregate polarization is the most abundant mineral, but kaolin also occurs.12 There is thus seen to be a profound difference from those coarse white marbles and garnet-staurolite mica schists which occur in the same structural belt in western New England.

Since the depth and deformation have been great in both cases, the difference can logically be ascribed only to a lack in the Pennsylvania region of heat and crystallizing solutions. This in turn suggests what is in accord with the other lines of evidence, that magmas have underlain the one region at moderate depth, and have been absent from the other.

[Daly13 reasons similarly from his work in British Columbia, and cites authorities for other localities showing that deep burial has produced metamorphism that is only partial or nil.]

(To be continued)

12 T. N. Dale, U. S. Geol. Survey, Bull. 275, pp. 75-85, 1906.

1 R. A. Daly, Bull. Geol. Soc. America, 28, 405, 1917.

ART. II. Note on Augite from Vesuvius and Etna; by HENRY S. WASHINGTON and H. E. MERWIN.

The problem of the constitution of the pyroxenes that contain alumina and ferric oxide-the augites-is one of the most puzzling and, in some respects, one of the most important that are presented by the rock-forming minerals. In an effort to aid its solution, I have made during the last few years a number of analyses of typical augites from Italian volcanoes, in the lavas of which augite is one of the most constant and most characteristic minerals. The study of these is not yet complete, and several more analyses remain to be made. But having recently completed two analyses of augite from Vesuvius and Etna, of which Dr. H. E. Merwin has determined the optical and crystallographic data, it seems to be advisable to publish the results as a slight contribution toward our knowledge of this important group of minerals. This seems to be the more justified as, notwithstanding that the species was based first on the crystals from these two volcanoes, we have as yet no satisfactory or modern analyses of them.

AUGITE FROM VESUVIUS.

Vesuvius has long been noted for its pyroxenes. Beautiful diopsides are found in many of the ejected blocks of Somma, and loose crystals of augite are among the products of many of its eruptions. The crystals studied here were obtained from the bottom of the crater, in part by me in June, 1914, and in part by Dr. A. Malladra, Director of the Osservatorio Vesuviano, during the same spring. For his kindness in sending me the material for study I would express my sincere thanks.

Occurrence. The crystals are found, either loose, and entirely or almost entirely free of scoria, as at many other volcanoes; or as phenocrysts in a highly vesicular leucite tephrite, which was being ejected in small amount from the orifice at the bottom of the funnel during my visit to it.1

The crystals are mostly of the usual, well-known, simple forms, such as are figured by Dana2 and in t text

1 A. Malladra, Rend. Acad. Sci. Napoli, November, 1914;

Day, Bull. Geol. Soc. Amer., 26, 375, 1915.

2 Dana, System, Figs. 16, 17, and 18, page 354, 1892.

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