USA > New Hampshire > Grafton County > Littleton > History of Littleton, New Hampshire, Vol. I > Part 2
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The peculiarity of such of these rocks as occur in Littleton is that they are traversed by lines of mineral arrangement called
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History of Littleton.
foliation, and the material may be cleared readily by the applica- tion of blows with steel utensils, hammers or chisels. Such rocks are termed schists, because of their easy splitting, and the arrange- ment can be called a crystalline lamination. Most schists possess banding that is unmistakable. These granitic masses in Littleton are imperfectly foliated, - so much so that different geologists will call them granite or gneiss, according to their predilections. Now granite has tendencies to cleave where the foliation cannot be perceived to exist by the eye, but may be present, so that some hesitation in deciding upon the presence or absence of foliation is pardonable. My present belief is that all these rocks are true granites rather than schists.
When this tendency to split was observed by the geologist of twenty-five years ago, he had before him the conclusions of his instructors that schists occupied the place of strata. Alternating bands of strata would have varying composition. The action of thermal influences with water would cause the molecules to rear- range themselves according to their affinities, and thus to form crys- tals, which would be as different in respect to coloration as were the original strata. The earlier geologists saw no way in which these crystalline lamina could have been formed except through the metamorphism of sediments, and hence foliation was said to be identical with stratification, only that sometimes one set of planes might cut across others. On studying the phenomena of cleavage, it became apparent that lines of structure perfectly com- parable with strata could be superinduced. It is the result of pressure. Suppose this admitted fact be applied a little further. Let us take a mass of granite just formed, still somewhat plastic. The constituent minerals lie in every conceivable position, perhaps well expressed by the statement that no two of the flat minerals lie in the same plane. Now let pressure be applied to this plastic bunch. All the flat minerals will be made to lie at right angles to the force exerted, and consequently parallel to one another. When an attempt is made to break the rock, splitting will follow the lines of arrangement of the flat minerals. If the pressure has been free to act for a long time, genuine foliation will be the re- sult. Hence it is possible to understand the origin of schists pos- sessing no trace of sedimentary origin. It will be easier to believe the granitic rocks of Littleton originated in this way than from the alteration of sediments. If the foliation is distinct, however, the rock is a gneiss rather than granite.
In entering upon the descriptions of these granitic areas it is assumed that they are all of igneous origin, and that their folia-
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The Geology of Littleton.
tion has been induced by pressure ; that they are not altered sedi- ments, although metamorphism has acted vigorously upon clastic rocks in other parts of the town, - in fact in districts adjacent to these granites, because the source of the heat is thus understand- able. Pains have been taken to record the positions occupied by the foliation, partly because of the habit acquired when these were supposed to represent sedimentation, and partly because they give information as to the direction of pressure.
PORPHYRITIC GRANITE. - Studies of the crystallines show a grouping of material in concentric rings around a nucleus. The porphyritic granite of Littleton may constitute the nucleus around which a finer-grained granite is enwrapped. The chief part of the area is towards the north, outside of the town limits. The interior core is an oval-shaped area of about four square miles in the adja- cent corners of Littleton, Whitefield, Bethlehem, and Dalton. The rock is of medium grain, filled with crystals, up to two inches in length, of potash feldspar (orthoclase), whence the significance of the term " porphyritic " or " spotted." The feldspars are often twinned, the plane of twinning corresponding with that of the foliation of the mica. The reversal of one-half of the twin changes the posi- tion of the cleavage planes, so that one part is clearly, and the other indifferently, reflected, and thus the crystals are conspicuous. Part of the rock is foliated, in which case the large crystals are disposed along the foliation planes ; other portions show no ar- rangement of any of the minerals. The ground mass is made up of the three usual mineral constituents of granite, - quartz, feld- spar, and mica. The mica is commonly the black variety, called biotite ; but in Littleton there is more than the usual supply of the white variety known as muscovite. Oligoclase may be present as well as orthoclase for the feldspar. The quartz is always amor- phous, so far as I have observed. Where the large crystals of feldspar are badly formed, they may be somewhat lenticular in shape, and the attendant mica disposed like eyebrows, so that one may imagine a ledge filled with staring eyes. Noticing this peculiarity, the Germans call this rock the Augen, - eye gneiss. There is often, also, a considerable iron in the rock, whose decay imparts a rusty color to the ledges.
In Europe and Canada the augen gneiss has been ranked as Archean. For that reason I called this rock Laurentian (= Ar- chean) in my report, and represented that the thirty areas of it known to exist in New Hampshire might have been the primitive land areas of the continent. With a changed view of its origin, it may still be regarded as thus ancient in some localities, for
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History of Littleton.
igneous rocks constituted the whole of the Archean terranes. This rock has also been erupted in post-Archean times, so that by the mineral character alone we are not warranted in deciding upon the age.
At Alderbrook, in company with the late Dr. T. Sterry Hunt, I made an attempt to determine the possible disposal of the min- erals in certain planes, which might be termed strata. We found, first, nearly horizontal masses with no variation of mineral com- position ; second, an alternation of coarse gneisses ; third, fine feldspathic layers, more irregular than the others. The predom- inating dip of these several sheets was 75° S., 40° E. It seemed at the time as if this arrangement might correspond to stratifica- tion ; and if so, it would represent a downward dip reappearing on the north flank of Mount Lafayette, thus constituting a syn- clinal axis ; and it was so figured in the report. Vol. II., Plate VI., Fig. 7.
At this same locality the rock has been much decomposed, so that when a ledge has been cut through it is found to be made up of loose blocks, as the softening and removal of the granite adja- cent to the joints has separated the fragments from union with one another. To the west of Alder Brook is a precipitous hill of the porphyritic granite, very conspicuous as seen from the village of Bethlehem. It is known as Bald Hill, and is immediately adja- cent to Mann's Hill. The foliation at the back of Bald has the dip of 70° N., 75° W., making an anticlinal with that at Alder Brook, and nearly parallel with the position of the adjacent mica schist. In the low ground towards Round Pond the boulders of this rock are extremely numerous.
GRANITIC GNEISS. - The porphyritic granite is encircled by a granitic gneiss, which represents the southwest terminus of a large terrane reaching as far as Milan. A band of mica schist inter- rupts the direct continuity of this gneiss from Mann's Hill ; but it is supposed to exist beneath the schist. The most important por- tion of this rock underlies the village of Littleton north of the Ammonoosuc, extending west as far as to the cemetery. The dip of the foliation is greater on Mann's Hill than upon Oak Hill, or in the village, it being 75° in a general northwesterly direction in the former, and about 40° in the latter locality. At the reservoir on Palmer Brook there is a ledge with the high dip, also along the railroad near Apthorp. Hornblendic layers occur on Mann's Hill ; and both there and in the village pieces of mica schist appear included in the gneiss. Hence the granite is probably of later origin than the adjacent Coos mica schists, from which the frag-
11
The Geology of Littleton.
ments have been torn. Further study may indicate the existence of a mass of granite, the porphyritic inside and the gneissic out- side, which is independent of the larger mass in Whitefield and Jefferson. The Littleton gneiss was ranked in the State report as a part of the common or Lake Winnipiseogee gneiss.
PROTOGENE OR BETHLEHEM GRANITE. - Quite early in our studies it was found convenient to give a local name to a mass of granitic rock sparingly foliated, and characterized by the presence of chlorite, talc, rotten mica, or other decomposition products. This rock is protogene, and the local name of Bethlehem was applied to it. The area touches Littleton in its southern corner. To prop- erly understand the structure one needs to note that the mass has an elliptic shape, occupying the chief parts of Bethlehem and Car- roll, and that the foliated planes dip at a high angle several degrees west of north. It was supposed in the report, following the idea of a sedimentary origin, that the structure was that of an inverted synclinal, the dip being somewhat to the west of north. The dip is vertical with the strike, N. 58° E. along the railroad opposite Apthorp, 75° N. W. on the east side of Mount Eustis, 55º N. 20' W. at South Littleton, and a few degrees less at North Lisbon. At the southwest part of the area are inclusions or pieces of dark schists imbedded in the granite. They are apparently pieces of the bordering mica schists, broken off by the disturbances con- nected with the intrusion of the granite. It is presumed that many of the inclusions have been incorporated into the liquid mass, while all have been more or less altered by the action of the heat.
According to the report, there are four leading varieties of rock in this area : First, granite made reddish by abundant flesh-colored orthoclase, with a chloritic mineral in place of mica and amorphous quartz ; second, fine-grained gneiss ; third, gneiss with porphyritic crystals of feldspar ; fourth, mica or chlorite schist with very little feldspar or quartz. Magnolite and epidote are not uncommon. Dr. Hawes remarks, concerning these protogenes, that in the thin sections some hornblende may be seen, and that the little plagio- clase present is much altered. Sometimes a handsome variety carries green spots, in the centre of which are scales of biotite, indicating that the latter was the original mineral. The green decomposition product is epidote.
This granite has been thought to represent Laurentian gneiss. Prof. J. D. Dana, who was a thorough advocate of a late age for most of the rocks of this vicinity, was convinced that some of the gneisses along the railroad must have been Laurentian because of
12
History of Littleton.
their resemblance to known rocks of this age elsewhere. As will be seen later, the Niagara and related rocks have been uptilted by this granite at South Littleton and North Lisbon ; hence it will be proper now to modify the earlier conclusion. The rock has never been stratified, and the pressure inducing foliation was directed in a direction between north and northwest.
HYDRO-MICA SCHIST GROUP. - If one examines the geological map of northern New England and Canada he will observe two important belts of green schistose rocks centrally situated. One starts in southern Massachusetts west of Connecticut River, passes almost directly north through Vermont just east of the Green Mountains into Canada, and then turns easterly, continuing to Gaspé. This terrane is repeated upon the west side of the Green Mountains in northern Vermont and Canada. The second belt commences near Bellows Falls, continues almost uninterruptedly along Connecticut River to Woodsville, where it expands and increases till it occupies nearly the whole breadth of northern New Hampshire. From thence it continues to the Gulf of St. Law- rence parallel to the other area. Littleton is situated upon this second belt.
The rocks consist of hydro-mica and chlorite schists, sand- stones, quartzites, argillitic schists, bands of argillite, dolomites, limestones, diorites, protogenes, hornblendites, and some others. The whole assemblage has a greenish tint, insomuch that Dr. S. W. Hawes was disposed to restore the old name of Greenstones for the group. For local names the usage has been varied. Sir W. E. Logan proposed three terms, - Levis, Lanson, and Sillery, - all of which combined were spoken of as the Quebec group. The first three of these names I applied to the rocks of the first belt, in the published New Hampshire State map, as they stretched southward into Vermont from Canada, following Logan. It ap- peared to the later Canadian geologists that Logan misunderstood the structure of these rocks in Canada, and hence his successors have explained the order of arrangement differently. They avoid the use of the three local names and speak of the terrane as Cam- brian, and to some extent pre-Cambrian. I made no attempt to correlate Logan's divisions in the eastern belt, but devised new local names ; calling the lower part Lisbon, the upper Lyman, and a still third band of auriferous conglomerate. In the first two annual reports I used the general name of " Quebec group " for these greenstones, recognizing the equivalency of the rocks with those farther west. I think nothing more is said about this area before the preparation of the final report, where the name Huro-
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The Geology of Littleton.
nian appears. In the first blush after the discovery of Logan's misinterpretation, the attempt was made to correlate these green rocks with their petrographical equivalents located upon the north side of Lake Huron, to which Logan had already given the local name of the lake. For this reference I was obliged to follow the leadings of certain Canadian geologists who were familiar with the rocks of the eastern townships of Canada, as well as with those farther west. At the present date those who have been studying these rocks, both to the north and south of New Hamp- shire, are divided in their views of age, - some finding them to be Cambrian, and others, following essentially the early opinions of Logan, making them to be Lower Silurian. The absence of fossils prevents a closer correlation.
Petrographical studies enable us to separate, as either of igne- ous or metamorphic origin, quite a number of the rocks named above. They are the diorites, protogenes, and hornblendites. They had at first been esteemed as essential constituents of the group, particularly as they are also abundant in the Huronian country. They are wanting in much of western Massachusetts, so that it is natural that the same strata there should be regarded as of a different age. Hence the presence of either of these igneous rocks shows us simply what kind of agency has been at work, and they do not necessitate reference to any particular age. These igneous rocks were grouped with the Lisbon terrane in my report. Now they might receive a separate coloration, as of a dif- ferent class.
Quite early in my studies I found the name applied by my prede- cessors to this central belt to be a misnomer. They were called talcose slates, having talc for its essential constituent. Now talc is a hydrous magnesium silicate. Average samples of these green- ish greasy rocks in Vermont were found to be hydrous aluminum silicates, and hence not properly talcose. Unfortunately, the pre- cise mineral present is not well known, because it is so indefinite in composition, so that it is not easy to find a name to take the place of talc. Under these circumstances, Prof. J. D. Dana pro- posed the term of hydro-mica instead of talc ; and for the present, it may be employed when speaking of the petrographical nature of the rock.
The Lisbon group includes properly the various greenish schists and sandstones, the latter commonly altered. The Lyman group was intended to designate, first, a massive light-colored or white schist, whose original color must have been some shade of drab ; second, a slaty rock of related color, with an argillaceous odor ;
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History of Littleton.
Dr. Hawes called them argillitic schists. The white schists are often entirely composed of elongated pebbles.
More than half of the township of Littleton is underlaid by these green and argillitic schists. My published map represents the whole of the northeast portion of the town, from Mann's Hill across to Connecticut River, as composed of the Lyman rock. A broad strip of it makes up Palmer and Wheeler hills, and passes southwesterly through Mormon Hill, and through the town of Lyman. Two or three other short areas of the Lyman group appear north of Partridge Pond, and the continuation of Gardner Mountain across to Waterford, Vt. The space enveloped by the Gardner Mountain and Palmer Hill ranges is referred to the Lisbon group, occupying rather a larger space than the other division. I cannot pretend that these divisions are marked by hard and fast lines, nor that the structure is well understood. Perhaps a few words about the character of several of the bands may best describe the geology of this terrane, largely quoted from the State report.
The western half of Littleton consists mostly of the Lisbon group. This development is characterized by the predominance of chloritic and green schists. The Gardner Mountain area is characterized by the presence of cupreous schists, in two localities, two hundred rods apart, which at one time were exploited for copper. The rocks of this mountain range are partly hydro- micaceous and partly argillitic, dipping 60° S. 70° E. Similar schists, standing vertically, are associated at the Quint copper mine, about a mile and a half east of the eastern Gardner Moun- tain belt. In general, the rocks from J. Bowman's, near Lower Waterford bridge, to W. Redwood's, a mile and three quarters east of the Upper Waterford bridge, are chloritic, with seams of calcite, usually perpendicular, with a northeast strike. At Mulli- kin's saw-mill the green schists are traversed by a trap dike, and some of the rock is conglomeratic, of the Lyman group. The rocks are similar on a hilly road from the saw-mill to near the slate quarry, or as far east as to D. Robbins' house. The green schists are continuous southerly from the saw-mill to the heights east of Partridge Pond. The map also shows a range of the Lyman schist northerly from Partridge Pond to Connecticut River. Near the town-house 1 is the boundary between the gray- ish green schists and protogene. The former may be two miles wide along the main road from the village to West Littleton. Other outcrops of these schists appear between the town-house
1 Old town-house near Fitch place.
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The Geology of Littleton.
and the Wheeler Hill cemetery. Bands of slate holding large nodules or bosses of quartzite occur east of Wheeler's. There are hydro-micaceous schists on the west side of Wheeler Hill. Near the summit it is more argillitic, carrying a little copper, with bands of a chocolate color. There are more green schists on the south side of Cow Brook, near R. Moore's, with the strike N. 50° E. ; also farther east upon Palmer Hill of the county map. The same schists occur on both south and north sides of Morse Hill.
A well-marked band of the Lyman schists enters Littleton from the northeast corner of Lyman. The rock is apparently a con- glomerate, in which the pebbles have been elongated, and display their fragmental character only upon weathering. It adjoins the fossiliferous strata at the head of the middle branch of Mullikin's or Rankin's brook. To the west and north of the lime quarries, near Parker's Observatory, this same schist is well developed ; and later theoretical views would make us regard it as a silicified argillite, much like the novaculite of Fitch Hill.
The State map represents another Lisbon area along the east side of Blueberry Mountain, reaching nearly to Palmer Mountain. Portions of it have been covered by the alluvial deposits of the Ammonoosne River. They pass into what was called the " Swift Water series," in the report on the hills west of South Littleton.
IGNEOUS BANDS CONNECTED WITH THE HYDRO-MICA SCHISTS. - These are the hornblendites, diorites, and protogenes, formerly thought to have been stratified and essential constituents of the terrane. The last-named occupies the most space. It may be seen in the notch north of Fitch Hill along the Waterford road, between one and two miles from the post office. It may also be followed up Fitch Hill in contact with the fossiliferous limestone, and along the western base of the Blueberry range for another mile. It is abundant the first half of the road up to Kilburn Crags. It occurs also on the east side of Blueberry Mountain back of the J. K. Corey place.
Diorite adjoins the Niagara slates on Fitch Hill, and has altered them at the point of contact into novaculite. It follows the ridge southerly, and is fully two hundred feet wide where it crosses the road up to Kilburn Crags, between sandstone and slate. There is a little hornblendite along the east flank of the Blueberry range, which is the obvious continuation of the more extensive nodular outcrops of the same material in the central and north parts of Lisbon. The true character of these igneous rocks will be dis- cussed farther on,
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History of Littleton.
SILURIAN AND DEVONIAN STRATA. - Under this heading are in- cluded the Coos mica schist and quartzite, the Niagara limestones and slates, sandstones and argillites. No fossils have yet been discovered in the mica schists. The name of Coos was applied to an associated group of quartzites and mica schists with staurolite, extending entirely through the State from Massachusetts to Can- ada. They are first seen in the hill west from South Littleton, whence it crosses the Ammonoosuc and rises into Mount Eustis. It then sinks beneath the river again at Apthorp, and rises into Mann's Hill, adjoining the porphyritic granite, and thence enter- ing Dalton. As fragments of these schists have been included in the several granites, it is believed the group was elevated at the time of the protrusion of the igneous masses. A greater elevation of the strata seems to have been thus originated in the hill west from South Littleton. The strata usually dip seventy degrees in a northwesterly direction, with variations due to the proximity of the granites. Micaceous quartzites abound in the bed of the Ammonoosuc in the village and near Apthorp. The exact junc- tion of the mica schist and granite may be seen in a railroad cut east of Apthorp. Staurolite is present in it upon Mann's Hill, where are also bosses of hornblendite and granite veins. Near the Dalton line some of the beds are calcareous. A little to the south of Littleton stauroliferous argillites show themselves. These were regarded as belonging to the same Coos series in the State Report. The mica schists with staurolite border the protogene granite on its south side, extending to the edge of Bethlehem along Indian Brook, and are supposed to be identical with the Mount Eustis belt, but pushed southerly by the intrusion of the protogene.
SWIFT WATER SERIES. - Adjoining the mica schist on the west in the south part of the town are considerable thicknesses of a whitish mica schist with siliceous layers, not readily referable either to the Coos or Lyman groups. They are of more conse- quence in the next town southerly. In the printed report they were referred to the Swift Water division of the hydro-mica schists. If one follows the south line of the town westerly from the railroad, he finds these schists exposed west of the Ammo- noosuc adjoining the Coos rocks. They are best developed where the road crosses the town line, near the P. H. Padelford place on top of the hill. Some of the schists are chloritic, associated with conglomerates made up of flattened pebbles interstratified with hornblende schists. These are followed on the west by the inde- terminate whitish schists. These all have a very high dip north-
17
The Geology of Littleton.
west. They occupy a sort of plateau, and dark slates succeed them as you climb Blueberry Mountain. Farther north and south a sandstone, limestone, and conglomerate outcrop between the schists and dark slates. The reason of their absence at the town line is unexplained.
SYNCLINAL STRUCTURE OF BLUEBERRY MOUNTAIN. - In the printed report considerations were presented in the attempt to understand the relations of the argillites of Blueberry Mountain to the adjoining rocks, to show that they were of Cambrian age, and that the fossiliferous limestones flanking them on both sides must be limited outliers, although apparently dipping into the mountain in the same manner. Our recent studies satisfy us that the structure of Blueberry Mountain is truly synclinal ; and hence these fossiliferous rocks must be older, and as they are of Niagara age, the slates must be still newer, - Upper Silurian or Devonian, perhaps best expressed by the term "Helderberg." As to the structure, the terrane in Bath and Lyman is admittedly synclinal ; so that no change in it would be looked for in Little- ton. Secondly, sections are now complete across the Blueberry range near the south town line, from the head waters of Mullikin's Brook to South Littleton, from the slate quarry to the Ammo- noosuc River, and farther north, all of which seem to involve the basin structure. Thirdly, the disappearance of most of the slate in the notch for the Waterford road, two miles west of the village, and its reappearance farther north, seem to imply the removal of the upper terrane by erosion. If the structure were anticlinal, the breadth of the slate should be greatest at the lowest point.
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