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Crossing Mink Pond is a gray, friable mica schist holding in profusion reddish staurolites and garnets, the locality heing one well known to mineralogists. The average dip heing 56°, tbe thickness must he 3,300 feet: This band is followed by the same garnetiferous slates which occur upon the
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GEOLOGY.
south branch of the Ammonoosuc. Stauro- lite is less abundant in this than in the previ- ous hand, and it is almost wauting in the west- ern portion. With an average dip of 59°, this slate must be over 3,000 feet in thickness.
The next division I call the Swift Water Series. It contains first, quartzites and sand- stones, 1,769 feet in thickness, resting upon the Coos group. This hand contains an au. riferons vein. Sceond, Hornblende schist 310 feet. Third, schist, concealed by drift, 240 feet. Fourth, Scbists and slates 242 feet. I now divide the Huronian into two parts, the Lisbon and Lyman groups. The first, on the section line, is composed first of talcose conglomerates 756 feet ; second, eupreous talcose schist, 3,539 feet. The Lyman group en the section consists of whitish schist con- glomerates 200 feet. The last group is thick- er than appears in this section, on account of a downthrow. These strata dip west, and are repeated iu Lyman, so that we have evi- dence of the existence of a synclinal axis. The cupreous schists contain much more cop- per on the west side of the synclinal, on Gardner's mountain. At about the summit of this group is an interesting band of quartz- ose conglomerate, generally containing traces of gold, from 10 to two hundred feet thick. Being quite persistent it will prove of great value in mapping out the dislocations of this district. In one case it has been shifted lat- erally 1,300 feet, and with it, of course, the ad- joining members.
In Coos county large masses of stratified diorite and serpentine characterize tbe Hu- ronian. The diorites form mountains like Mt. Carmel 3,711 feet above the sea. An- other memher is a peculiar rough hornhlende rock. extending to the north heundary from Colombia. Both steatite and dolomite occur in various localities along the Connecticut, and. near the third Connecticut Lake.
CAMBRIAN .- The discussions about the value of the Cambrian series are leading geologists to assign to this place in the col- umn a thick mass of sediment, usually with. eut fossils, and largely argillaceous in cbar. acter. We may for the present place here the following groups. 1. Mica schists of southern New-Hampshire. 2. Merrimack group including argillo-quartzites in Coös county. 3. Coös group. 4. Clay slates. 5. Mt. Mote conglomerates.
MICA SCHISTS .- These occur on the west side of the Exeter syenite range. They were formerly supposed to be a repetitien of the Merrimack group on the west flank of an anticlinal. They had also heen confounded with the White Mountain series. They are separahle from the latter on account of the absence of feldspar and andalusite. Their areas are given only in part. Large heds of granite, and a range of quartzite heleng to this series, Narrow ridges of it show the place of synclinals in the gneiss.
MERRIMACK GROUP .- These recks consist of micaceous quartzites, sometimes mica schists and more or less argillaceous mem- hers, with interstratified heds of granite. In New-Hampshire this formation lies to the
east of the Exeter range of syenite. It con- tinues into Massachusetts, following the Mer- rimack valley to Lowell, and continuing south- westerly heyond Worcester.
Allied to them in character are certain ar- gillo-quartzites in Northumberland, Stratford, Stark aud Berlin. There is little beyoud mineral character to correlate these two areas. The northern one has been disturbed by the movement of the Labrador rocks in such a way as to suggest a later age for them. Ob- servation indicates that a narrow band of a slaty rock will be more broken up and thrown out of place thian adjacent massive strata, so tbat the amount of disturbance may not nec- essarily indicate greater antiquity. These silicious rocks have heen pressed so as to stand vertically against precipices of compact feldspar, supposed to consist of horizontal strata. But the scbists do not pass under tho feldspar, and hence we suppose them to be inore recent in age. An extensive area of schists northwesterly from Umhagog Lake is probably referahle to one of the above two groups. Latterly it has been suggested that this group helougs to tbe Huronian.
Coos GROUP .- This consists of quartzites, mica schist, hoth with and without staurolite, argillaceous schist, clay slates with garnets and ohscure mica, possibly phyllite, calcare- ous mica schist, hornhlende rocks and vari- ous sandstones. My third New Hampshire report gives four sections across this group, in Lishon, Orford, Lyme and Hanover, with an average thickness of ahout 10,000 feet. Suhsequent investigations modify all our puh- lished statements respecting this group. The limestone and gneiss of the sections must be eliminated ; the proof of which is. very evi- dent. The gneiss in Hanover underlies the same succession of quartzite, staurolite, mica schist and horublende rock in two or three localities along the same section line, and thus all the rocks are repetitions instead of one unbroken series. In Haverhill, the gneiss with limestone underlies the supposed Coos quartzite, with a strike differing from that of the latter as much as thirty or forty degrees. I do not find any regular gueiss in the Coös group anywhere in the State. It is a curious fact also that there are extensive ranges of what seems to he the Coös quartz- ite resting uncomformably upon the gneiss, without any connection with mica or horn- hlende schist. They must continue to he ranked as Coös till we have evidence to the contrary. The Coös group may also embrace the "calciferous mica schist " of Vermont. The original definition of this group express- ly excluded the latter rock. Further study will he required to make this position a sure one.
CLAY SLATE .- This is common in Lyman and Bath. A study of its structure over this area shows it to he normally synelinal, and resting upon the Lyman group chiefly. This structure is hest recognized in Bath. On passing northerly, the hasin is broken up into fragments hy the rising up of tho un- even floor, the segments indicating irregu- larly the synclinal. But, after reaching the
neighborhood of the Dodge gold mine, the strata are monoclinal, and continue thus till they disappear beneath the Helderberg. The case is analogous to those in Berkshire County, Mass., described recontly by Pro- fessor Dana. Analysis of this slate in Ly- man gave Professor Scely, silica 72.98, per- oxide of iron 6-35, nlumina 5.99, magnesia ·36, potash 5-61, soda 9.92 = 101.21. Thus this slate resembles the common schist of the Lyman series. Possibly it was derived from the decom position of the latter.
Tho synclinal form of these slates confirms the general theory of structure in this neigh. borhood, already presented. For, if this area is a hasin, it must lio upon older strata ; and, if both sides of the slato are flanked by a similar succession of strata, the latter must he relatively older. In fact, this slate is flanked first hy the Lyman schist, and that in turn by the Lisbon group. On tho south- east, tho latter joins on to the Coos series, and on the west it comes in contact with the same slate, in both cases newer rocks; but ultimately gneiss is found after one or more inferior undulations. The slate range on the west is supposed to extend to Bernardston, Mass., on West Mountain. On one section it has a thickness of 1,500 feet, with a maxi- mum of 1,800.
MIT. MOTE CONGLOMERATES -. These ure apparent upon the Mote mountains in Alha- ny and Mt. Pequawket in Chatham. A brief sketch of this structure of Pequawket will hest illustrate the character of the group.
The same granite which appears at the Flume, is found in the Green Hills, and all along through Conway, at Kiarsarge village, and in the lower part of Pequawket. Above this the Albany granite occurs upou all sides most distinctly. It is not abundant on the south and east, but very characteristic. On the south, it crops out on the hillside below the slate. About five hundred feet abovo the south hase of Pequawket, and in the old footpath (that of 1840), occurs a ledge of clay slate, directly above the granite. This formation does not scem to extend far, as it is not found in either of tho new paths up the mountain, and a very short distance from its lower houndary we pass beyond it and come upon the Mt. Moto group, of which the up- per two thousand feet of Pequawket appears to consist, viz., an igneous felsite, full of peb. bles. The greater portion of the included fragments are angular, slaty, lying at all aa- gles, and range in size from an inch to a foot in diameter : They wero all taken from Coös slate just helow, whence it is clear that tho Coos group is the older of the two.
SILURIAN .- Two groups of rock may he referred to tbis ago, the Swift Water Series and the Helderherg. The first have heen noticed in the description of the section pas- sing through Lisbon and Lyman. Tbe lat- ter series is of the greatest consequence he- cause fossils have been discovered in it.
The discovery of Helderberg fossils in New-Hampshire was announced as follows in a telegram addressed to Dr. T. R. Crosby, President of the Dartmouth Scientific Asso-
ciation : " Littleton, N. II., Sept. 28, 1870: No longer call New Hampshire Azvic. Silu- rian fossils discovered to-day." Tho dispatchi was read the same evening to the Associa- tion, at a regular meeting. Not long after- ward. E. Billings of Montreal reported upon the specimens. The corals appeared to be Favosites, basaltica and Zaphrentis, probably the same with those occurring . near Lake Memphremagag in Canada. The erinoids were all small. Mr. Billings found nothing that would localize the horizon more definite- ly than the general term of Hellerberg. The Owl's Head locality, fifty-five miles dis- tant from Littleton, in Canada, has furnished the characteristic Atrypo reticularis and oth- er species of the Upper Helderberg, en- abling the Canadian geologists to ropresent upon their maps several narrow strips of the Upper Helderberg limestone.
An allied rock bas long been known at Bernardston, Mass. It was first described by my father in the Massachusetts Report of 1833, with a drawing of the crinoidal stems. It has generally bren considered as the equivalent of the Upper Helderberg or Cor- niferous limestone of New York, on account of the presence in both of enormous crinoid- al stem-fragments.
The Memphromagog and Bernardston de. posits lie upon the opposite sides of the same formation-the calciferous mica schist group of the Vermont Report, and Upper Silurian (supposed Niagara) of Sir W. E. Logan's Report-and separated by a distance of 165 miles. The mica sebist is probably an older formation than the Helderberg, lying in a trougb of clay slates, the latter constituting the. floor of the fossiliforous heds. These slates may be Lower Silurian or Cambrian, judging from general considerations. No fossils yet appear in thein. Tho enleareous schists carry a few obscure crinoidal frag- ments at Derby, Vt., which are of no value in tho indentification of strata.
At first sight, one would declare that thero is no similiarity between the Littleton and Bernardston rocks. After considerable stu- dy of both localities, I find a few points of resemblance, perbaps as much as we have a right to expect in synchronous deposits more than a hundred milos apart. In our studies, we often look for exact resemblances in re- mote localities. Perhaps it is better that the 'connecting tie he discovered with difficulty, in which case the conclusions may he moro suroly established. The surroundings at Littleton are different from those at Ber- nardston. Tbo series rests upon a colorite rock or hard green hydro-mica scbists, close hy gneiss, and a whitish, soapy schist. At Bernardston, the underlying as well as the overlying rock is quartzite, and in the neigli- borhood are the mica and staurolite schists just described as tbe Coos group.
In order to make the descriptions of these fossiliferous rocks clear, I introduce a small map of the region where they occur and a few characteristic sections. The course of tbe sections is indicated by lines on the map, fig. 4.
GEOLOGY.
Figure 4.
LANDATT EXPLANATION
SHIT MATUA GROUP.
PORPITRITIC GNUSB. EHE
BETHLEHEM.
HOLDENSONG.
CLAY STATE.
USBON GROUP.
LYLAH
ONBSS
WA
The first section is at the north-east extrem- ity of the map, extending from Palmer to Burnham's Hill, nearly one and three-fourths mile. Palmer Hill is composed of Lyman schist, dipping 78º N. 28° W. In passing to the depression (which is in reality a water- shed for the streams flowing northerly and soutberly), the strata first stand perpendicu- lar ; they then dip north-westerly ; nnd finally several measurements in a distance of tbirty rods gave S. 34° E., 80° S. 10° E., and 85°, S. 35° E. The rock here (Closson's) is an in- durated slate, chiefly siliceous. Next we pass up a bill, over the Lishon schist perhaps, dip- ping 80°, S. 15° E. On top of the bill there is a siliceous rock, which from different observers bas received the names of sandstone and buhr- stone ; it dips sometimes northwest, hut per- haps oftener to the southeast. On the north slope of tbe bill, the sandstone varies in posi- tion from about 80° S. 8' E. to S. 8° W. This rock ean he followed a mile northeasterly across tho road going eastward to Mann's Hill, and then is supposed to turn and follow up the hill to the southeast of Burnham's bouse, and to continue soutb- west to Parker River. It has its maximum development on the east side of the basin, constituting what
Figure 5.
1
THAT
would be called a mountain range in many parts of the country.
Overlying the sandstone, as I suppose, is tho fossiliferous limestone. It has been exca- vated at several places quite extensively, and burnt in a contiguous kiln. It is usually of a light drab color, somewhat brecciated, and the fossils are not conspicnous, but upon search tbey prove to be considerably abun. dant ; the thickness varies from ten to fifty feet. On the north side, tbe limestone forms a precipice of twenty feet, in consequence of excavations. The overlying slate is seen to best advantage in descending the hill toward Littleton. It is rather dark, soft, splits read- ily and contains fucoids and markings like Chondrites, and dip southeast.
Fig. 6 shows the most important of the sections, partly because it is near the travel- ed road to the Connecticut River west from Littleton village. It is one mile and three- eighths long. Tbe gneiss is the Oak Hill de- posit, and is in place one-eighth of a mile north of the section, with a dip of 35°-40° N. 20° W. Tbe chloritic rock appears next. It is close by the road, opposite the last house hofore reaching Parker Brook, and can he traced along the ridge extending northeast for one-fourth of a mile. The dip is 60° N. 50° W., with n somewhat higher dip down the slope.
The fossiliferous limestone follows immedi- ately. The first layer seems to conform with the wall rock. At the kiln, which is not fifty feet from the base, it dips 60° E. 5° S., and also westerly. Hence there is a small anticlinal axis. Directly at the kiln no fossils were oh- tained ; they come from a dark layer with a westerly dip nearer the brook. The Zaphren- tis and the Favosites with small crinoidal frag- ments are found here.
The nlluvium of Parker Brook intervenes and conceals the rock for an eighth of a mile perhaps. On the southwest side there are several outcrops of limestone-some of them containing coral masses. A slaty inass witb no cleavage is mixed with it. The limestone near the first house on the west side of Parker Brook is bluish, and was at first supposed to belong to the Lisbon series-as it is not fos- siliferous. It has been excavated for a kiln in years gone by. Recent researches indi- cate tbat the whole of this range extending into Lisbon, is of Helderherg age. The strata have somewbat of a zigzag arrange- ment, which need not be described in detail.
Directly beyond the brick kiln we find tbe chloritic rock in its perfection, dipping in the same direction with that nlready noted, hut at a steeper angle, and the range is only thirty rods wide. At a turn in the road, slate of less width, seemingly vertical, appears, and we discover imbedded in it two feet in thickness of compact crinoidal limestone. This identi- fies tbe slate with the deposit upon Fitch Hill, a quarter of a mile to the southwest,
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Yig. 5 .- Sec)loo from Paluer Will through Burbbsod's Ilme quetry; 1, Lyman group: 2, Palmer BIJL; 3, Closon's hotso; 4, Llebop group; 5, Fatt Hill: 4, Quarta ; 7, Helderberg Ilinestobe ; 8, Blaje; 9, Burnham's house ; 10, Quarts,
TOWER
15
GEOLOGY.
Figure 6.
.
1
Fig. 6 .- Socilob along carriage road westerly from Littleton vitlage. 1. Green achlatu; 2. Chlorit ~; a, deklarberg alote ; 4, Chlo- rilo ; 5, Parker Brouk : 6, Holdetborg Condis ; 7, Lline quarry : d, Chlorite rock ; 9, Goein (auppomed)
Figure 7.
10
Plg. T. Section aouthely lium Hich's house. 1. 4'hlor le: 2, Quartz: 3, Bintoe ; 4, Vossl'a in linicaluue, a, Swiem, {, Limestone; 7, Conglomerniu ; 8, SIliceous (Onestato ; 9, Hurablende; 10, Sandalone.
The next section in fig. 8 is three and three-eighths miles long, and passes over more strata. It com- mences high up the early course of Mul- liken's Brook, erosses Blueberry Hill, and terminates a sbort distance north of
whore the Pentamerus is found. The mingled slate and limestone extend up the hill and then across the ridge.
The chloritic rock re-appears on the section at a fork in the road, and continues uninter- ruptedly for three-eighths of a mile, dipping 75°-80º northwesterly. This would give a thickness of about 1,900 feet of strata. Fig. 6 shows the order of the rocks from Fitch's house to the summit of the hill. The first rock seen above Mr. Fitch's is the chlorite rock, running N. 65° -- 70° E., and containing a layer of white quartz. In the pasture the strike changes to nearly east and west, and this fact is made certain by the position there of the white quartz, which curves with the chlorite but may bo a little nearer the Helderborg after the bend is pass- ed than before. This is confirmed by examnin- ing the rocks east of the Helderberg range. On fig. 6 above, there are thirty rods of chlo- ritic rock east of the slate range, but on Fitch Hill, in consequence of the transverse course of the slato, it lies on the southeast of the chlo- rite altogother, as shown in fig. 7. To the southwest there is another outcrop of this range of chlorite, because the Helderberg is cut off by it, but the fossiliferous seam again covers it when the low ground is reached, and the hard rock is seen no more.
Furthormore, the contact between the Held- erberg and chlorite on Fitch Hill is not a di- roct succossion or interstratification, since there has been a sliding of one rock over the other. The removal of the turf revealed a slickensides between the two. The limestono is followed by forty or fitty feet of coralline slate ; thirty or forty feet of friable conglom- erate, white when weathered, like the Oriskany sandstone of New York, the quartz pebbles being of the size of kernels of Indian corn. Next is a bluish, somewhat siliceous limestone nf two sorts. Tben follows considerable tough, massive hornblende rock, with nn signs of stratification and a strange associate of the Pentamerus limestone. On the very apex of the hill is a sandstone weathering white, but gray in the interior. It dips ap- parently 50° east of north. The section is ahout half a mile long.
Figure 8.
Fig.S .- Section from Moltiken's Brook lo North Lisbon. 1, Lyman group, bear G. D. Shinto's; 2, llelederberg alntes 3. Conglomerate ? : 4, Dark alates; 6, Lisbon group ; 6, Mica schleta ; T. Hornblende rock ; 5, Conglomerate Swift Weter !; 9, Goole
Figure 0
Flg. O .- Section up South Branch, N. Llatson. 1. Unelos: 1. Conglomerate : 3, Blotes : 4, CungInmerate : 6, Blates ; 0, Lisboa group; T, Cooa group, stourollin ulates.
North Lisbon, reaching the gneiss. At the beginning is the Lyman instead of the Lisbon group, though the latter would appear if the section had been elongated half a mile. Near G. D. Shute's house and "Indian Rock," theso schists dip 85º N. 20° W. The cast bordor of this group dips 80º N. 30° W. It weathers whitish, presenting a chalky aspect at a little distance. Along the carriage road succeeding is an extensive range of llelder- berg slates and limestones containing Favo- sites. Tbe strata stand perpendicular, run- ning northeast. On a tributary stream, near C. Hastings's houso, is a fine exposure of grit, slates and calcareous beds, greatly resembling fossiliferous strata in Maine and New York, but they yielded no relics of life in a half-hour's search. This series of strata forms a steep cliff 70 or 80 feet high, which can be fol- lowed a mile and a half to the slate quarry. The country at the hase of the cliff is every- where a swampy forest not intersected hy roads, so that its exploration is not inviting.
Passing up the hill, there is a coarse con- glomerate. Near the top of Blueborry IIill are slates with the course N. 65° E., and ir- regularities which may be explained by sup- posing cleavage planes to be present having a different striko from tho strata. On the crest of the hill the slates dip 70° N. 25° W. This continues about half a mile on the line of section, or as far as I was ablo to travel upon it. There is room enough for the double thick ness of slate seen in fig. 7.
The eastern slope has not been examined throughout. About half way down I have twico examined ledges apparently of the Lis- bon group dipping toward the hill. Mr. Huntington travelled over the remainder of the section, and his specimens seem to indi- cate, first, tho mica schists of the Coös group, (6) followed by considerable horn blende rock, (7) and lastly by a conglomerate (8) with whitish cement and pobhles of the size of buck-shot. This rock stands on edge on the top of the hill next the Ammonoosuc River, and, with the mica and horn- blende schists, is perhaps our . T Swift Water series. The horn blende may connect with a large mass of the same rock a mile southwest, it being in
contact with Helderberg there. The horn- blende may correspond with the same rock on figs. 5 and 6, The mica schists evidently be- long to the Eustis Hill series, at the south of Littletou village, possibly disconnected from that outlier by erosion.
The gneiss at the southeast end is part ot. the area known as " Bethlehem gneiss," or rather the common variety upon its border. The mica is black, and the feldspar often scanty. The position differs from that of the other rocks. Its normal position is about, 40° clip toward the north, both the inclination and course varying from those of the other strata that have been cited.
This section, if protracted, would cross an- other interesting Helderberg area; but for the sake of clearness, I will add a small sec- tion (fig. 9) with greater horizontal scale, situated about a quarter of a mile to the southwest, erossing the Ammonoosue nearly at North Lisbon railroad station and passing up the "southi branch." The gneiss dips 36° N. 35° W., at the " Lead mine." Next is a coarso conglomerate, seen in the field and un- der the bridge, dipping 65°-70° N. 10° W. As there is a general resemblance between this and the conglomerate of the Lisbon group, it was not till the reccut discovery oľ extensive Ilelderberg strata that these ledges at North Lisbon appeared to belong to the Paleozoic series. Tho materials of the pehbles are white and bluo quartz, hydro-mica schist or Lisbon group, two or three gnoisses, Coös slates and calcareous masses, with an argillo-micaceous pasto. Somo pebbles are a foot long. They are usually slaty but not distorted.
Crossing the river and walking over twenty rods of gravel, we coine next to a inore inter- esting locality in the south branch valley. The first ledge, back of the last house on the read, is micaceous slate with calcareous layors, cut by an obscure igneous dike. The strata dip 45º N. 20° W. Beneath aro fifty feet of coarse eonglomerate, containing, in addition to the pebbles under the bridge, pieces of the mica schist of the Coos group, without stau- rolite. These Helderberg conglomerates are estimated to be 500 feet thick. Tho slates next observed have a higher dip. They are followed by indurated slates dipping 50° N. 10° W. They are traversed by beauti d ribbons of banded trap from half an inch to three inches in width, which jump and curve in a fanciful way.
The next series evidently belong to the Lis- bon group, having essentially the same strike and dip with the last mentioned beds. They extend for about twenty-five rods along the stream. The rock is a gritty hidro-mica sebist mueb indurated. They terminate at a great bend of the stream, whero tbe water passes through a narrow gorge of clay slates containing staurolite and garnet, and dipping 60° N. 17º W. These ledges extend easterly for twenty-five rods, after which they are covered with boulder clay for a great dis- tance. The Lisbon group just mentioned, has heen traced across to the west of Streeter
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