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A more natural explanation is to regard the thinning out of the volcanics and overlying slates as due to their removal by denudation, previous to the deposition of the Blaini. This view derives some support from the presence in the Blaini boulder bed of angular fragments of volcanic ash, which must have been indurated and converted into solid rock previous to their transport to the locality in which they are now found.
Termination of the ridge between the Naira and Bangál valleys.-Along the termination of this ridge, where it slopes down to the Tons, and in the Naira valley, there is exposed a grey slate series containing a band of blue limestone about 300 feet thick. These resemble the slates and interbedded limestone of Southern Jaunsar which were described by me as "Upper Chakratas." West of the Tons they appear to pass under the "Lower Chakratas," and the section upwards from the latter is a normal one. This apparent reversal may be due to disturbance, but there is every possibility that the section in Jaunsar on which I based my conclusion was inverted. The question of which of the two, the slates and limestone or the red quartzites, is the newer, remains to be decided by further survey.
Unconformity at the base of the infra-Krols in the Valley of the Minas gádh (Suinj R. of map).-The whole northern side of this valley appears to consist of limestones; possibly near the top some other series may come in, for I did not examine the hillside, but certainly the greater part of the northern side of the valley, near the Tons, is composed of a limestone series, which I see no reason to doubt is the same as that of the Deoban hill. The limestone extends south of the stream and can be seen faulted against the purple quartzites of the "Lower Chakrata" series. At the head of the valley both limestone and quartzites are overlaid by a band of black carbonaceous slates and limestones, which is also seen in the Gerwáni hill, resting on the grey slates that overlie the volcanics. This carbonaceous series can be very distinctly traced along the hillside, and, though it appears to be faulted in the Minas valley, does not seem to be cut by the fault which separates the limestone and quartzite series lower down, at any rate not to the same degree. This would point to the boundary fault being of great age, and to a complete removal of the Deoban limestone south of it previous to the deposition of the black carbonaceous slates, and consequently to a great unconformity at their base. These black carbonaceous slates can be traced into continuity with similar beds in the Chepal valley, where there can be little doubt that they represent the infra-Krols of the Simla region.
The Mandhali beds of the Chor and Chepal.-On the eastern side of the Chor mountain there are several exposures of a boulder bed, very similar to the Blaini conglomerate in physical characters, but without the characteristic associated limestone. The most southerly exposure is on the north side of the Minas valley a little below the hamlet of Dim (Demi). The boulder beds are here interstratified with blue limestone, a feature also noticed in the Mandhális of Jaunsar, and lie between the massive, presumably Deoban, limestone and the carbonaceous slates. This "conglomerate" is not continuous in this position, as it is wanting near the village of Deothali (Thotali), but it is present on the Cheti (Baiti) ridge.
Between this and Chepal the rocks are too disturbed for their structure to be determinable in a rapid survey, but east of Chepal the boulder beds recur in the
same position as further south, viz., between the massive limestone and carbonaceous slates. The beds are a good deal cut up by faults, which, added to their variable nature, renders it difficult to determine a really characteristic section. One which was roughly measured by me gave a band of conglomeratic slates, underlaid by 100 feet of non-conglomeratic slates, below which were conglomeratic bands Occurring with quartzites through 200 feet, while 50 feet below these came a band of pink limestone, resembling the Blaini limestone.
This exposure is referred to by Col. McMahon, who declared that "it is beyond all reasonable doubt that the rocks here seen are the Blaini rocks." I think it is beyond all reasonable doubt that they are the same as my Mandhális of Jaunsar, which they resemble very strongly in physical character and in their superposition on a massive limestone series.
Whether the Blaini and Mandháli rocks are of the same age or not I shall leave for a separate paper on the boulder-bearing slates of the Himalayas, but it is necessary here to remark that I could find no proof of unconformity between the boulder beds and carbonaceous slates; but the irregular appearance of the former points to an unconformity of both on the Deoban limestone. The same is proved by the presence of fragments of the latter rock in the former, and in this it agrees with the Mandhális of Jaunsar.
Before leaving this subject I must notice that in the exposure east of Chepal there is a small patch of a rock which very strongly resembles a volcanic ash. The rock is exposed on the very crest of the ridge and is almost immediately cut off by a fault; what remains is very much decomposed, but I notice it, as this is the only case I have seen where a rock associated with the boulder beds has presented more than the most superficial resemblance to a volcanic rock.
The volcanic rocks of the infra-Krol series.—On the spur south of the Minas gádh, leading east from the Chor, in the Deora valley of Jubal, on the Narkanda-Sungri ridge and on the Lambatách ridge between the Tons and the Pabar, I found volcanic beds associated with the black carbonaceous slates. These beds differ in age and character from those of the "Lower Chakrata" series; the specimens have not yet been examined in detail, but, speaking broadly, it may be said that they are of a more decidedly basic character than the Lower Chakrata volcanics.
These are the same beds as are described from the Sutlej valley2 by Col. McMahon, who correlates them with the volcanics of Dalhousie and Cashmir.
The gneissose granite of the Chor.-As the Chor was deeply covered in snow when I was in that neighbourhood, I did little more than take a passing glance at the eastern margin of the granitic intrusion. The intrusive nature of the gneissose granite having been proved already, it is not necessary to consider this point in detail, but I may say that the manner in which the boundary of the granite cuts across the bedding of the adjoining sedimentary rocks, as well as the numerous inclusions of schist and quartzite, make it very evident that the rock of the Chor is a granite by origin.
I was, however, able to make one observation which has an important bearing on the mode of intrusion of the granite. On the spur south of the Minas gádh the
'Records, G. S. I., Vol. X, 210.
2 Records, G. S. I., Vol. XIX, 67.
black carbonaceous slates are overlaid by the volcanic beds noticed above, here changed by contact metamorphism into hornblende schists and mica traps. On the spur north of the Minas gádh no trace of these rocks can be seen, but in their place is an exposure of a rock which only differs from the porphyritic rock of the Chor generally, in that the matrix is highly hornblendic, and consequently dark coloured, thus throwing up the porphyritic crystals of orthoclase with great distinctness.
I do not see any possible explanation of these facts unless we suppose that the granite dissolved and absorbed the rocks, whose position it now occupies. On this supposition its locally hornblendic nature, where it replaces hornblendic rocks, is easily explicable, while the very slight disturbance of the surrounding beds, as well as the steady dip towards the Chor, are inconsistent with the supposition that the granitic intrusion was either the cause or consequence of disruption of the sedimentary beds. The gneiss series of the Upper Pabar valley.-In the upper reaches of the Pabar valley and its affluents there is exposed a series of beds which, whether we have regard to their lithological structure or their mode of origin, must be classed as a gneiss series. For the most part the beds are gneiss, but they vary in one direction to nearly pure felspar, in the other to a very slightly felspathic mica schist; some beds are schistose greisen, and there are a few of metamorphic quartzite whose sedimentary origin is easily recognizable. The foliation is parallel to the bedding planes, and the whole is most palpably metamorphic, using that term as opposed to intrusive, and without reference to whether these rocks ever were or were not ordinary sediments, such as those the slates have been formed from.
Many of the beds of gneiss contain porphyritic eyes of orthoclase, sometimes two or three inches in length. As regards internal structure, they resemble the porphyritic crystals of the gneissose granite, being composed of a single twinned crystal of the Carlsbad type, but they differ in their external form, which is lenticular, and in their invariable arrangement, with their greatest diameter along the plane of foliation. Doubtless it was by fusion of this rock that the intrusive porphyritic granite originated.
The position of this rock is very clear, for the beds lie very flat for the Himalayas. It unconformably underlies a series of red quartzites, which, near the Búran (Borenda) pass, are overlaid by beds containing hornblende schist. I have little doubt that these represent the "Lower Chakratas" and overlying volcanic beds, the lithological similarity between the quartzites being especially striking.
Arkose beds of the Lambatách ridge.-On the Lambatách ridge there is exposed a series of beds presenting many points of interest which, owing to the coming on of the monsoon, I was not able fully to investigate. The beds consist in part of the fine grained felspathic quartzites which extend into Bawar, and were there described by me as the Bawar quartzites. But below these comes a great thickness of more or less schistose beds containing granules of felspar. In the Kotigadh (Kunjado R.) the rock is at first sight difficult to discriminate from the porphyritic granite, which it resembles also in its mode of weathering. But on closer examination it is seen to decompose more readily, and a close examination will generally show that the felspar consists of broken crystals, while not infrequently small pebbles may be detected. Another feature which separates it from the gneissose granite and unites it to the felspathic grits is the abundance of granules of pale blue transparent quartz.
These rocks pass upwards into black carbonaceous slates and limestones, associated with volcanic beds, which in all probability are the same as the infra-Krol carbonaceous slates. If this be so, the arkose cannot have been derived from the porphyritic granite, which is found intruded among carbonaceous slates on the Chor and in the Deora valley, but must have been derived directly from the archæan gneiss. It seems probable that these arkose beds indicate a severe climate, as it is evident that the disintegration of the rock from which they were derived must have been more rapid than the decomposition of its constituent minerals. This view receives some confirmation from sections exposed in the road cuttings in the Deota forests; some of these beds of coarse grit have scattered through them boulders of quartzite, ranging from a foot and more in diameter. With so coarse-grained a matrix this does not prove glacial origin, unless it could also be proved that the beds were not of subaërial origin; for large boulders may often be rolled along the surface of a much finer deposit, where the latter is formed by shallow streams. But, as there is no direct evidence of a subaërial origin of the felspathic grits, it seems natural to take these boulders, combined with the undecomposed felspar, as indicating a severe climate.1
It may be noticed that the arkose beds appear to hold much the same relation to the carbonaceous slates as the presumably Mandháli boulder slates do to the carbonaceous slates of the Chor and Chepal. The latter, there is every reason to believe, are of glacial origin.
Crystalline and Metamorphic Rocks of the Lower Himalaya, Garhwal and Kumaun, Section II, by C. S. MIDDLEMISS, B.A., Geological Survey of India.
In the last number of the "Records" I described Dudatoli Mountain from a petrological and structural point of view. The present paper will be devoted to a short account of some ancient Rhyolites and associated rocks which adjoin the Dudatoli area on the east. Their geological importance depends partly on the fact that they are the first representatives of an acidic type of lava that I have met with in British Garhwal, partly on their situation among a set of formations sharply marked off from the neighbouring schistose area, and chiefly on the circumstance that among them exists a transitional form, connecting petrologically these ancient acidic lavas with the gneissose granite of the Dudatoli ridge. This is the first time that any of the gneissose granites of the Himalaya have been shown to be connected with a subaërial lava flow: and the coincidence seems to finally clinch the argument and set at rest the controversy concerning the eruptive character of the gneissose granite. Strictly speaking however, it only demonstrates that a portion of the gneissose granitic material was drawn upon by volcanic vents; and, as this 'I have found that gneiss and granite disintegrate into felspathic sand, in which the felspar is undecomposed, at elevations of 14,000 feet and over in Ladák. I have never seen a material which could consolidate into arkose at the lower elevations, up to 10,000 feet, of the outer Himalayas.
material may have come from a source vertically far above where the Dudatoli ridge now is, the deeper-seated magma now represented by the Dudatoli rock may never have had much of a demand made upon it by the volcanic action above, to rush into eruption, and so may never have possessed much motion relatively to the intruded rock. I will describe these erupted lavas, and the formations among which they occur, by reference to a locality where I first hit upon them.
LOBAH VOLCANIC ROCKS.
The map facing page 142 of the last number of the "Records," at its east margin, is contiguous to a great faulted boundary running nearly north by west as far as the Dewalikhal pass, and then veering further west as it skirts the north-east portion of the Dudatoli massif. This fault can be traced for 20 or 30 miles forming a great dividing line between the old schistose series among which the gneissose granite is insinuated, and the younger set of lavas and more nearly related formations with which the gneissose granite is approximately contemporary. A few miles from the fault these younger formations, in the vicinity of Lobah, have a fairly steady dip towards the east-north-east; but near the fault they are forced into a few close folds, with subordinate faulting, nearly parallel with the great fault itself.
The strike of these rocks may be put down as very nearly N.N.W. to S.S.E. They, therefore, cut directly across the strike of the schistose series, which is roughly W.N.W. to E.S.E.
The lowermost of the younger set of formations, east of the fault, is a limestone of dark blue-grey colour, and massive appearance; only differing from previously described limestones of this type by the presence of nodules of chert in some of its upper layers. This formation peeps out from underneath the volcanic rocks in longer or shorter anticlinal domes, and is well exposed in the stream beds which join the Ramganga from the east. I hazard nothing at present concerning its age. A short thickness of glassy looking quartzite is superposed in some sections.
A great unconformability, with attendant conglomerate, ushers in the volcanic rocks. The conglomerate, which it will be convenient to call the Lobah conglomerate, varies considerably within a few miles of outcrop; and vertically also it changes very rapidly. Its strongest feature is a large, well-rounded, torrent-boulder bed; the pebbles being from a few inches to a foot in diameter. They are chiefly quartzite, of that hard and glassy kind found immediately beneath the conglomerate. I found no pebbles whose constitution could be called a quartz-schist. A few limestone pebbles were occasionally present. The whole is coherent, as a massive and exceedingly hard rock, with a little cementing material of coarse quartzose and slightly calcareous substance. In certain localities the pebbles are scarcer, and the basal conglomerate is then a conglomeratic, faintly schistose slate, or ashy slate. It is sometimes absent altogether, and the limestone is directly overlaid by the faintly schistose slates. South of Lobah, however, the section is complicated by the introduction of a more decided volcanic element. Along with the larger pebbles there appear angular fragments, and the matrix of the rock changes and assumes a hard dark-green compact aspect suggestive of a felsitic nature. This gradually frees itself from the rounded pebbles, the angular fragments remaining, and more and more