tural distinction between this province and the Laurentian of Canada appears to rest upon the lesser depth to which erosion has planed and the resulting lesser destruction of the batholithic roofs.

RELATIONS IN NEW ENGLAND BETWEEN BATHOLITHIC AND METAMORPHIC LIMITS.

Preliminary Statement.

The regional metamorphism of New England is marked both by a thorough recrystallization of the sediments and a folding and mashing. The intrusive rocks are also involved to a greater or less extent. The generality of this relation, both for this and other regions, has caused them to be linked together in geological theory as direct cause and effect; the deformation of deepseated rocks being regarded as the cause of their regional metamorphism. This conception developed, however, before the igneous and intrusive nature of the basal gneisses was recognized, and even yet the importance of deep-seated batholithic extension has not been considered in the theory. It is desired here to test this prevailing conception against another which would regard recrystallization as largely and directly related to batholithic heat and emanations, and the folding and mashing as a related but partly independent process, due to crustal compression, but going on most readily in the weak and recrystallizing roofs of batholithic chambers.

The Pre-Newark Floor of the Connecticut Triassic. To test this question, let the region be considered which lies in Connecticut between the Triassic of the Connecticut Valley and the dying out of the Appalachian folds in the Hudson Valley. The crust movement at the close of the Newark sedimentation gave a regional tilt of about 20 east to the rocks of the Connecticut Valley, and a regional tilt of about 20 west and northwest to the New Jersey area. Extensive faulting also took place as a part of the movement. The western margin in Connecticut, the eastern in New Jersey, are not in general, however, fault boundaries. They are the two slopes of a geanticlinal arch upraised at the beginning of the Jurassic period. The fault movements, however, partly neutralized the effects of the tilt, so that the actual elevation of

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this axis in western Connecticut is unknown. less, the breadth and dip of the crust blocks show that the elevation was great, notwithstanding that peneplanation had ensued by the beginning of the Comanchean.

The Connecticut Valley is the foot of the eastern slope of this Jurassic anticlinorium. As a result of later base-levelling across this, on going west from the edge of the valley one passes progressively into rocks originally deeper and exposed by successive cycles of postNewark erosion. On the edge of the Connecticut Valley, as Davis was first to note, is exposed the old Triassic floor upon which the basal Newark sediments were laid down. Here there has been no erosion since the midTriassic beginning of the Newark sedimentation. It is physiographically the nearest to the surface of the earth in the Appalachian revolution of any part of western Connecticut. What, then, is its character? In the northern half, two granite bosses outcrop, each about four miles in diameter. The northern especially is associated with more or less fine-grained intrusive amphibolite. The country rock is a lustrous sericite schist, becoming coarse-grained where penetrated by pegmatite dikes and dikelets. In the southern part of this border zone, the Prospect gneiss is intersected. This is a belt exposed for more than thirty miles, with an average width of two miles, and striking slightly diagonal to the contact. It consists of sheets of slightly gneissoid coarse biotite granite porphyry. The texture is highly variable, and it seems to have been intruded in successive sheets. It does not widen in passing away from the Triassic floor into what was presumably greater original depth. It appears, then, to have been a great dike intrusion, rather than a batholith. South of this occurs a dark slate, the Orange phyllite, containing quartzitic and calcareous beds. This is the least metamorphosed sedimentary formation in western Connecticut. South of this is found the Milford chlorite schist, extending to Long Island Sound. This is a hydrothermally altered series of basic sheets, strongly resembling the Keewatin chlorite schists, though of Paleozoic and probably of late Paleozoic age.

The topography of this area is in detail rugged, sheets of feldspar porphyrite (now slightly altered) having been injected into a previously mashed series of much the same composition. The older and thoroughly chloritized portions are probably only slightly older, as shown

by the similarity in composition. They show that extensive deformation and hydrothermal alteration was going forward at the time of their formation. They have the character and relations of a superficial series whose basic nature marks the first intrusion of the batholithic magmas. Such series, as seen more clearly in the Cordilleran field, accumulate as thick surface flows and breccias. as the first stage in the batholithic cycle. As they thicken, injection into them takes place, as well as outpourings on the surface. If any of these are ancient surface flows and breccias, the evidence is, so far as the writer has observed, now destroyed, and it is only the latest intrusive sheets which show much of their original nature. These are thin and somewhat limited, showing in places chilled margins on both contacts. The alteration has been a hydration and pyritization accompanying and following mashing by which chlorite, serpentine, quartz, calcite, and pyrite have been developed. The pyritization proceeded along the joints of the more resistant sheets, showing that jointing persisted in the unmashed portions. Rare, thin seams of pegmatite with tourmaline are found. The assemblage of phenomena show alteration at only moderate depth.

The changes in passing from central Massachusetts to Long Island Sound along this resurrected Triassic floor show a progressive rise through the crust from the broad areas of Williamsburg granite, which Emerson regards as of Carboniferous age, to comparatively superficial rocks and possibly surface flows, presumably of the same igneous cycle as the granites to the north.

Now, the degree of deformation does not notably change. Cleavage and close folding is dominant in the southern as well as in the northern part, but the degree of metamorphism is conspicuously different. Surrounding the granites, feldspathization and pegmatization have occurred. Garnet, staurolite, and sillimanite are developed. The sediments are transformed into coarse and lustrous muscovite schists, the basic rocks into amphibolites. In the south, removed from the batholiths and presumably nearer the ancient surface, the argillites are black slates, somewhat crumpled and lustrous, but such as, if occurring in a more homogeneous formation, might have supplied slates of commercial quality. The impure limestones have apparently retained their carbonic acid in the presence of quartz and kaolin. The

basic igneous rocks have suffered hydration and have surrendered their lime to the carbonic acid which pervaded them. The degree of anamorphism appears, therefore, to be here conditioned upon depth and contiguity to batholithic masses, not upon the intensity of the deformation.

The Section across Southwestern Connecticut.

It has been shown that in passing westward from the Connecticut Valley one crosses a Jurassic anticlinorium leveled by later erosion. One transects also the structures imposed by earlier deformations, so that the actual depth at which occurred the metamorphism of the rocks of any given locality is difficult to state. It is clear, however, that the great faults which cut diagonally across the Connecticut Valley at Meriden largely die out on entering the western metamorphic province. This is shown by the moderate offsets of the western margin as compared to the great offsets and repetitions of the strata in the middle of the valley. Doubtless distributive faulting in the western province occurs and some greater faults may be concealed by the complicated structures. The Pomperaug Valley, holding Triassic strata in the midst of the anticlinorium, shows that it is by no means a single great structural arch. Nevertheless, the regional dip of the Triassic floor gives strong suggestions that on passing west from New Haven to Bridgeport or Derby one goes progressively into regions once deeper in the crust. It is as if the railroads were inclines at slopes of 5°, 10°, or 15° leading from the upper world downward into the abyss. The exposures are best on the New Haven-Derby trolley line. What, then, are the changes to be observed in the nature of the rocks?

At the eastern contact, the least altered sheets of porphyrite are found and quartz infiltrations are rare. One to two miles west, the cleavage is much more pronounced and uniform. Considerable silicification is present and quartz lenses occur in discontinuous strings, having deformed the chlorite schists by the power of their crystal growth. One passes then into the Orange phyllite, a soft black crumpled slate. Some three miles farther west, the first sheets of the biotite granite porphyry appear, interbedded vertically in the highly foliated sediments. Within a few hundred feet of the

first thick sheet, quartz infiltrations become noticeable, then fine-grained garnets enveloped in muscovite. Within a hundred feet the sediments become transformed and at the contact are lustrous but fine-grained schists. In between the granite sheets, the texture of the schists becomes coarse and sparkling. Still farther northwest, sheets of granite and pegmatite become more abundant, the schist becomes feldspathized, crumpled, and of maximum coarseness, cyanite and garnet become abundant, the proportion of magma increases, and the rocks pass finally into truly igneous masses. In the region of Danbury the granite gneisses envelop and intrude the Stockbridge limestone, and it is found to be transformed into a coarse white friable marble.

The beginning of the intense anamorphism on this section is clearly a contact effect of the first granite sheets, here with vertical attitude. Beyond, they show evidences of being part of an injected and intensely altered batholithic roof. The metamorphism, then, is here primarily related to the presence of magmas, but is secondarily related to depth. Deformation is the adventitious factor which has affected all the section and produced cleavage with hydration in the upper and cooler portions, cleavage with dehydration in those portions which are deeper, hotter, and invaded by magmatic emanations.

The Section across Northwestern Connecticut.

The writer has made a study of the geologic section on the northern state line of Connecticut from the Green Mountain anticlinorium, here represented by the southern Berkshire Hills, westward across the Taconic synclinorium into New York State. The Laurentian Becket gneiss, with its included metasediments, and the Lower Cambrian Dalton schist outcrop in the anticlinorium. The rocks are overturned and overthrust upon the Stockbridge marble of Cambro-Ordovician age. This outcrops in the picturesque Housatonic Valley, here some eight miles in breadth and marking the structural limb between anticlinorium and synclinorium. The axis of the latter holds synclines of the resistant Berkshire schist, of upper Ordovician age. The structures throughout are intensely deformed by minor and major folds and by mashing. The foliation planes are in general inclined eastward at a dip of about 30°, showing an intense regional overthrusting.