BULLETIN OF THE GEOLOGICAL SOCIETY OF AMERICA

VoC. 42, PP. 467-480; 9 FIGS. JUNE 30. 1931 ------1------1---

KAMES AND KAME TERRACES OF CENTRAL MASSACHUSETTS 1

BY THOMAS C. BROWN

(Head before the Geological Society December SO, 1930)

CONTENTS Page Introduction ...... 467 Location of the kames and kame terraces...... 468 Jackson Avenue 420-foot terrace...... 468 Kame terrace near Whitmanville...... 470 Kame terrace west of Templeton...... 470 Kames of Millers River Valley near Orange...... 471 Boulder-bearing kames and terraces...... 473 Terraces of the southern part'of Nashua Valley...... 473 Terraces of the North Nashua River V alley...... 475 Interpretation of kames and kame terraces...... 475 Salisbury’s interpretation of the New Jersey kames...... 475 Interpretation of Massachusetts kames and kame terraces...... 475 Concentration of cobblestones on kame surfaces...... 476 Graphic illustration of the origin of kames...... 477 Summary ...... — . : ...... 478

I ntroduction The numerous valleys of north central Massachusetts are bordered by more or less continuous terraces at elevations varying from 200 feet above sealevel in the lower part of the Nashua Valley northeast of Pepperell to more than 1,000 feet in the upper reaches of Millers River Valley north of Winchendon. These terraces vary in areal extent from mere discon­ tinuous fringes in some of the valleys to broad sand plains a mile or more in width, such as the plains surrounded by the 260-foot contour south of Ayer and south and east of Shirley village; Many of these terraces have kames associated with them, either broad areas of knob-and-basin topog­ raphy like that of Bakers Brook Valley east of Fitchburg, or single scat-

1 Manuscript received by the Secretary of the Society January 5, 1931. (467) X X X — B u l l . G e o l . S o c . A m ., Vol.. 42, 1931.

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tered hillocks jutting out into the valley like those along Millers River west of Orange. During the past few years extensive road and concrete construction has brought about the opening of numerous sand and gravel pits in these sand plains and kames. As a result fresh sections of the interior have been opened up on a scale that gives the geologist an unusual opportunity to study the structure of these deposits. From the scores of different pits studied in the past few years, a few typical cases are here selected for careful description, and an attempt is made to explain their origin.

L o c a t io n o f t h e K a m e s a n d K a m e T e r r a c e s ■ JACKSON AVENUE 42O-FOOT TER RA C E Near the east end of Jackson Avenue, in the eastern part of Fitchburg, an extensive sand and gravel pit furnishes an excellent section of the 420-

F ig u re 1.— Sand Pit near Jackson Avenue, east of Fitchburg This illustration shows a section in the terrace along the western side of Bakers Brook Valley. The top-set beds of coarse gravel are horizontal ; the sands and fine gravels beneath them are intricately cross-bedded.

foot terrace on the west side of Bakers Brook. In this pit the working face is approximately 25 feet high. The upper 6 feet is composed of horizontally bedded coarse gravel with numerous pebbles and cobblestones 4 to 6 inches or more in diameter, all well rounded and fresh and nearly all of granite. Beneath this coarse gravel is at least 20 feet of intricately cross-bedded sands and fine gravels. Many of the beds are lens-shaped ; ^ others dip at variable angles and in various directions. These dipping beds are frequently truncated and covered by others that are practically

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horizontal. Aside from the top bed of coarse gravel, no bed or series of beds shows any consistent or persistent dip in any direction for more than a few feet. In the same 420-foot terrace, about 200 yards south of this sand pit, another excellent section was exposed by an extensive piece of grading in the northern part of Saint Bernard’s Cemetery. In reducing one of the rather abrupt natural terrace slopes to more gentle contours, the whole upper surface over an area of a half-acre or more was excavated by steam shovel and moved down the grade. The part excavated was in some places as much as 15 feet in depth and 50 yards or more in length. Examina-

F ig u re 2.— Section of Käme Terrace at Elevation of 820 feet, a Quarter of a Mile south of Whitmanville

This exposure, which is in a road gravel pit, shows clearly that the original bedding has been disturbed by slumping toward the valley since deposition, and that the surface slope is due in part to the settling of the beds and not wholly to erosion.

tions made at different times during the progress of this work showed that the structure of the sand plain here is identical with that of the sand pit farther north. The upper 4 feet or more is coarse horizontally-bedded gravel. Below this come cross-bedded sands and fine gravels, the sands predominating; the beds and lenses of material dip at comparatively low angles, but in almost every direction. There is no dominant direction of dip as in the fore-set beds of a delta; the bedding may better be com­ pared with that characteristic of kames, which has been graphically de­ scribed as “tumultuously bedded.”

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KA ME TERRACE HEAR WH1TMANVILLE A pit opened for road gravel in a kame terrace at an elevation of 820 feet, a quarter of a mile south of the bridge on the Whitmanville-Gardner road, exposes an excellent section of the terrace. Here again the upper beds are nearly horizontal and composed largely of coarse gravel, and the lower beds are sandy and irregularly cross-bedded. This pit was ex­ cavated to the valley margin, and shows clearly the internal structure where the terrace slopes down to join the valley floor (see figure 2) . The surface slope is due not to erosion, but largely to the slumping of the beds. This is clearly seen by following the massive bed of fine sand which

F ig u re 3.— Terrace west of Templeton This structure seems to indicate that the terrace was built up to a uniform level with horizontal top-set beds. Then through some unknown cause a portion of the terrace slumped down and the sag was later filled with fore-set beds. is shown in horizontal position near the right side of the picture. About one-third of the way across the picture this bed is dropped vertically a foot or more by a normal fault; in the next third of the section it dips at a considerable angle; and in the last third it is so disturbed and mingled with material from the overlying bed of gravel that its identity is lost. Erosion may have modified the slope to some extent, but it could not cause this mingling of the beds.

KAME TERRACE WEST OF TEMPLETON A sand pit opened during the construction of the State road through Templeton disclosed the structure shown in figure 3. This pit is one

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mile west of Templeton on the west side of Trout Brook and the south side of the State road, opposite the Templeton Cemetery. Only the upper part of the pit is shown in the figure. The arrangement of beds seems to indicate that this terrace was at one time built up to uniform level with horizontal top-set beds like those described in the previous examples but composed of finer material. Then these horizontal top-set beds sagged into the synclinal structure shown in the figure, and the sag was later filled with fore-set beds, bringing it once more to the terrace level.

KAMES OF MILLERS RIVER VALLEY NEAR ORANGE On the north side of Millers Eiver, one mile west of Orange, is a kame at an elevation of 560 feet, having the structure shown in figure 4. This

F ig u r e 4.— A Kame Ridge "beside the State Road one Mile west of Orange This illustration shows how the upper beds have slumped down the side of the kame and become crumpled and bent during the movement.

kame is composed largely of fine sand. The crumpling of the beds, at first glance, suggests pressure due to ice movement, but a careful study of the kame in its natural setting shows th at this crumpling is more likely due to the removal of support and consequent slumping. Half a mile west of this kame, at the same elevation and on the north side of the river but the south side of the road, is the kame shown in figure 5. During the reconstruction of the State road in 1930 this kame was used as a gravel pit and eventually was almost wholly removed. Several visits to the locality during the course of the excavation proved that the structure of this kame was throughout like that shown in figures 5 and

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F ig u r e 5.— Gravel Pit in Kame a Mile and a Half west of Orange This illustration shows how the internal structure is perfectly preserved in the middle of the kame but has been destroyed by slumping on either side.

F ig u re 6.— Close-up View of Margin of Kame shown in Figure 5 This illustration shows the transition from the well-preserved beds of the center to the slumped and disturbed beds of the margin.

6. The upper part of the kame is composed of horizontally bedded coarse gravel top-set beds, approximately 6 feet in depth. Beneath these are beds of sand and fine gravel more or less irregularly cross-bedded but in

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places showing a disposition to form fore-set beds either toward the center of the valley or downstream. Some of these fore-set beds are shown near the center of the figure. On the right or downstream side and also on the left or upstream side of this kame the beds have slumped down so that the materials are mingled and the identity of the beds is lost. As ex­ cavation proceeded toward the valley this margin of the kame also showed evidence of slumping.

F ig u re 7.— Gravel Pit in a Terrace west of Templeton A great number of large boulders occur in this terrace, causing it to resemble a terminal moraine in composition.

BOULDER-BEARING KAMES AND TERRACES Although most of the kames and associated terraces are composed largely of well-assorted sands and gravels, a number of them contain occasional boulders and some a great many, in such instances resembling moraines in composition. Figure 7 shows a pit in one of these terraces from which the sand and gravel has been removed for road construction and the boulders left uncovered. Throughout the whole region the terraces and kames show the external features and internal structure described in these typical examples. TERRACES OF THE SOUTHERN PART OF NASHUA VALLEY Crosby and Alden have described similar terraces in the southern part of the Nashua Yalley. Crosby2 came to the conclusion, as a result of

2 W. O. Crosby : Geological history of the Nashua Valley. Tech. Quart., vol. 12, 1899, pp. 312-324.

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his studies of the region around the metropolitan reservoir near Clinton, that these sand plains were built out into open lakes in the valley. “That these high level deposits of modified drift were, in the main, formed in standing water, and only to a limited extent by marginal streams, is indi­ cated by the considerable breadth of the plains at some points, and also by the more or less distinct depression which usually . . . separates the sand plains from the slopes of ledge and till rising above them. . . 3 Alden came to the same conclusion, for he says in regard to the ter­ races of the Clinton stage of Glacial Lake Nashua: “Drainage from the ice front contributed much, and the lake waters them­ selves accomplished more or less erosion of the deposits of the Boylston stage along their shores, so that probably the deposits described above filled the val­ ley from side to side almost if not quite up to water level. Indeed, the lake may have been entirely filled up so that in its place a stream meandered over a broad flood plain. The gravel deposits mark the final stages of the filling.” 1 Both Crosby and Alden believed that the ice-front was a gradually re­ treating one and had a lobe which projected southwestward in the Nashua Valley. The gradual retreat of this lobe to the northeast uncovered suc­ cessively lower outlets and gave rise to the successive stages of Lake Nashua. Both authors, however, recognized the existence of water-worked sand and gravel deposits which could not be explained by their theory of lake development. Crosby states: “My detailed study of the modified drift has not extended over the Groton and Fitchburg quadrangles of the topographic map, and I am not fully pre­ pared to explain the extensive plain or mass of modified drift having a nor- mal height of 400 to 420 feet, lying between the Fitchburg Railroad on the north and the North Nashua Kiver on the south.” 5 Alden also encountered difficulties, for he states: “North and northwest of Whittemore Hill, however, in the town of Lan­ caster, partly within the Quinsigamond quadrangle, occur similar pitted delta plains of sand and gravel at altitudes of 300 to 400 feet; that is, at levels some­ what higher than the last of the delta plains south of South Lancaster.” In a footnote he says: “Professor Emerson states in a personal communication that a study of the area to the north of the Quinsigamond quadrangle has made it appear prob­ able that these deposits are connected with the Clinton stage.” 8

* Crosby : Op. cit., p. 315. 4 W. C. Alden: The physical features of central Massachusetts. U. S. Geol. Survey, Bull. 760, 1924, p. 66. 5 Crosby : Op. cit., pp. 323-324. «Alden: Op. cit., pp. 69-70.

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TERRACES OF THE NORTH NASHUA RIVER VALLEY Studies conducted by the writer in the valley of the North Nashua River show that these deposits which troubled Crosby and Alden are of great areal extent and have an important bearing on any theory of origin of the so-called Nashua Lake deposits. Some of these have been briefly de­ scribed in two earlier papers,7 and a more comprehensive study is now under way. These studies have confirmed the work of Crosby and Alden in showing that the deposits were formed in bodies of water occupying the valley, but they have proved also that these bodies of water were relatively narrow marginal lakes surrounding a great mass of ice which occupied the central part of the valley. The present study of the kames and käme terraces confirms this finding, for the kame terraces are without question deposits laid down in narrow bodies of water held between the valley wall and the valley mass of ice, and the rounded hillocks or groups of hillocks represent sandy fillings in embayments or hollows in the mass of ice.

I nterpretation o p K a m e s a n d K a m e T e r r a c e s

SALISBURY’S INTERPRETATION OF THE NEW JERSEY KAMES We have in the Massachusetts kames precisely, the same sort of struc­ tures as those described by Salisbury from the glaciated area of New Jersey: “In mountainous regions, where the friction of movement was great, it some­ times happened that considerable masses of ice became stagnant during the dissolution of the ice-sheet. . . . Ultimately some of the valley ice lost its motion, but even after it became stagnant, it exerted an important, though passive, influence in determining the position of stratified drift deposits, and the forms which they assumed.” After explaining how the drainage along the sides of the ice mass would give rise to deposits of stratified drift banked against the ice, he adds: “After the ice had melted, these deposits of stratified drift constituted a sort of constructive terrace against the valley slope. . . . A kame terrace, then, is a terrace of sand and gravel, deposited by a glacial stream between valley ice (generally stagnant) and the rock slope of the valley. More or less isolated kames are sometimes associated with kame terraces.”8

INTERPRETATION OF MASSACHUSETTS KAMES AND KAME TERRACES The kames and kame terraces of north central Massachusetts differ from those in the New Jersey region only in the greater number of the

7 T. C. Brown: Report of the Committee on Sedimentation, National Research Coun­ cil, Bull. 92, 1930, pp. 84-86. Am. Jour. Sei., vol. 19, 1930, pp. 359-367. 8 R. D. Salisbury: Glacial geology of New Jersey, vol. 5, 1902, pp. 121-123.

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kames and the greater areal extent of the terraces. Some of the Mas­ sachusetts terraces reach a width of a mile or more, owing to the fact that they were developed in marginal lakes held at constant elevations for considerable periods of time, and not along the valleys of marginal streams. The irregularities of the terrace fronts and of the kame surfaces indicate in part the irregularities of the ice mass against which they were de­ posited, and in part the changes which took place when the ice melted. The irregular cross-bedding of the lower portions of the exposures indi­ cates that they were laid down against a slowly retreating ice wall. The slumping shown at the valley margin in figure 2, and on either side of the typical kame in figure 5, was caused by the melting away of the ice support and the consequent settling down of the original beds of sand and gravel.

CONCENTRATION OF COBBLESTONES ON KAME SURFACES Many of the smaller rounded kames of this region show at their sum­ mits an accumulation of coarse gravel and cobblestones. This feature is characteristic of kames in other regions and has led to the suggestion that these knob-like hills were formed at the mouths of ice tunnels from which subglacial drainage issued with great force. The coarse material is supposed to have been dropped at the tunnel opening and the finer material carried away by the outflowing water. The surface covering of coarse material on the kames in this region can be explained in a different way. These kames represent deposits in de­ pressions or embayments in a mass of ice along the margin of a glacial lake. As noted above, the top-set beds in these kame terraces and kames are almost always much coarser than the underlying cross-bedded mate­ rial. Thus when they were first formed coarse material predominated on the upper surface. Moreover, these sand and gravel deposits were left by the melting ice with slopes which equaled or exceeded the angle of repose for this kind of material, and for a long time they existed prob­ ably with little or no covering of vegetation; hence they fell an easy prey to both rain and wind, and a considerable part of the fine material which was originally mixed with this gravel covering was either blown away, washed down to a lower level, or carried to a near-by stream. In other words, the concentration of coarse gravel and cobblestones on the surfaces of these kames seems to be largely a secondary feature due to differential erosion and not wholly a primary feature due to the method of origin.

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GRAPHIC ILLUSTRATION OF THE ORIGIN OF KAMES Two diagrams are here presented to show the conditions which prob­ ably brought about the formation of these kame terraces and associated knob-like kames. In the first diagram, figure 8, is shown a portion of a narrow marginal lake, with an ice bay or enlarged crevasse in the side of the ice. The lake was probably well supplied with sediment, a part coming from the surface of the ice mass, but the greater part probably

Sand and gravel would fill this bay and, after the ice wall melted, give rise to a typical kame hillock.

contributed by the adjacent land. This material was spread out by the waves and currents of the lake, and any crevasse or embayment in the ice would be filled up at the same time as would the bottom or channel of the lake. Figure 9A shows a section across such a bay or depression in the

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ice after it was filled up to the level of the adjacent lake sediments. Even­ tually when the ice completely withdrew from the valley, the bay-filling would be left without the support of the wall of ice and it would slump down into the form shown in figure 9B. This hillock would then be attacked by erosion and would be slightly modified by the action of rain

F ig u r e 9.— Section across the ice Bay A :t Section across the ice bay shown in figure 8 while the ice was still in position. B : The same section after the ice melted and allowed the sand and gravel to slump into a rounded hillock.

and wind. The chief factor, however, in causing its present form was the ice wall which surrounded it when first formed.

S u m m a r y The sand and gravel plains of central Massachusetts, which have fre­ quently been referred to as delta plains, show the typical internal struc­

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ture of kame terraces and differ from them only in areal extent. This greater area is due to the fact that they were developed in marginal lakes held at constant levels for long periods of time. The internal struc­ ture of both kames and kame terraces shows that they were formed along the margins of stagnant masses of ice which occupied the valleys.9 Both the irregularities of the valley margin of the terraces and the knob-and- basin structures of the kames are due to the fact that the sand and gravel deposits were heaped against an irregular ice wall containing many crevasses, pits, and embayments. After the ice wall melted these de­ posits slumped into positions of repose and then became subject to erosion by rain and wind. Although the surface features have been somewhat modified by erosion, they were largely and primarily determined by the conditions under which they were formed.

8 See R. F. Flint: Bull. Geol. Soc. Am., vol. 39, 1928, pp. 955-984, for a description of similar terraces in the Connecticut Valley.

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