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coloured and rather argillaceous; the other chiefly red and usually sandy; it ranges from the Carnian to the

Norian. 3. An Upper Series particularly abundant in red and white

sandstones, mainly of Liassic age but extending into the Cretaceous in places.

This threefold division of the Indosinias is also adopted on recent geological maps of French Indo-China.*

C. Federated Shan States. In the preceeding number of these “ ('ontributions”, the Red Beds of the Northern Shan States, the Namyau Series, were dis

cussed at length, more particularly as regards The Namyau Series.

the identity of certain limestone horizons which they contain with the Liu-wun Brachiopod Beds of Western Yunnan and their alleged relationships with the Norian Brachiopod Beds of Northern Indo-China. At the same time a plea was made for an examination of the lamellibranchs from the Namyau limestones, in the hope that they might furnish better evidence of age than that based entirely on earlier studies of their brachiopod fauna.1 Unknown to the writer such an investigation was actually in progress then and Dr. F. R. Cowper Reed has now published descriptions of numerous lamellibranchs from two separate calcareous horizons in North Hsenwi. His paper must be consulted for details, but it may be noted here that one horizon is identical with other well known outcrops in North Hsenwi and Hsipaw and with the Liu-wun Brachiopod Beds, while its fauna suggests a Cornbrash rather than a Callovian or Lower Oxfordian age. The lamellibranchs of the second horizon indicate a Bathonian age. Thus the earlier view that these limestones belong to the Upper rather than the Middle Jurassic has to be abandoned, and Buckman's original opinion on the age of the brachiopods is now no longer in conflict with the results of Dr. Cowper Reed's researches on the lamellibranchs.

** La Chronique des Mines coloniales”, Vol. 7, No. 73, p. 141, (1938).
1 Rec. Geol. Sury. Ind., Vol. 71, Pt. 2, p. 203, (1936).
? Ann. and Mag. Nat. Hist., Ser. 10, Vol. XVIII, pp. 1-28, (1936).

Dr. M. R. Sahni has criticised the proposal of certain French geologists to lower the Namyau and Liu-wun limestones down to the Norian, and concludes as follows:

“Dr. Reed's description of the lamellibranchs, however, leaves no doubt as to the Jurassic age of at least part of the Namyau Series, and confirms the broader conclusions arrived at from a study of the brachiopods alone from the same series elsewhere. The Norianage theory of the Namyaus and Liu-wun Beds can, therefore, hardly be maintained, even on the evidence of the lamellibranchs, whose investigation Dr. Coggin Brown has rightly advocated ”.i

This more exact determination of the proper position of certain limestone bands of the Namyau Series, does not, in my opinion, finally settle the question of the age of the whole of the Red Beds of the Northern Shan States. The total thickness occupied by such calcareous horizons is insignificant in that of the whole ensemble, moreover, the division of the latter into two sections is a suggestion unsupported by any stratigraphical evidence while the separation of an upper portion as the “Namyau Shales” will bear no critical examination in the field.2 The “shales",

“shales ”, more often than not, are thin bands of red clay, occurring here and there, through several thousands of feet of what is essentially a great sandstone formation. How much of this is older, or what amount is younger than the Middle Jurassic, has still to be determined.

The Red Beds of Kalaw were also dealt with in the same earlier contribution, and, it only remains to add that as reconnaissance

surveys have been extended, similar rocks have The Red Beds of Kalaw.

been identified in other previously unknown

parts of the Southern Shan States. In the west V. P. Sondhi found them, as anticipated, further down the Panlaung Valley while he has also reported them from the extreme cast, in the area lying between Kengtung and the Siamese frontier3. No new evidence bearing on their age is forthcoming, though the publication of Dr. M. R. Sahni's paper on the supposed Cretaceous cephalopods has decided this palæontological problem. Yet there is still a possibility that both Kalaw Red Beds and Namyau Series might range into the Cretaceous period. For the moment, the former may be regarded as Rhætic or younger.

1 Rec. Geol. Surv. Ind., Vol. 71, Pt. 2, p. 220, (1936). 2 Rec. Geol. Surv. Ind., Vol. 71, Pt. 2, p. 228, (1936). 3 Rec. Geol. Surv. Ind., Vol. LXIX, Pt. 1, p. 59, (1935). * Rec. Geol. Surv. Ind., Vol. 71, Pt. 2, pp. 166-169, (1936).

D. Siam.

It is well known that the salt-bearing " terrains rouges

" of the Mekong Valley of the French Laos stretch to the west into Siam.

Prof. Jacob, for example, recalls Capt. Cupet's Captain Cupet's Ob

observations on the numerous salt efflorescences servations.

between Nongkai and M. Lakhon and how they are found sporadically still farther towards the south and perhaps to Korat.1 The statements of various geologists who have made traverses in Siam across these rocks will now be summarized.

Bertil Hogböm describes the formation as a mighty series of red sandstones, conglomerates, red and violet shales and thin lime

stone bands which attain their greatest extenBertil Hogböm, 1913.

sion on the Korat Plateau, continuing east into the Lower Laos and south into Cambodia. Brine springs and salt efflorescences are said to be as characteristic of these rocks as their red colour. While they are nearly horizontal, or only slightly folded, over the greater part of the Korat Plateau, in its northwestern corner, to the east of Utaradit and in northernmost Siam generally, the Red Beds have been affected by strong movements. Hogböm designated the age of the formation as Trias, though, as usual, there is no direct evidence of this. He adds, “I also encountered sandstones of obviously Triassic age where the Meping River enters the vast limestone highland south of Chieng Mai. These sandstones lie conformably on the Permo-Carbonian formation and have been seized by the same gentle flexures".2 It is clear from Hogböm's work that two distinct red formations occur in Siam as they do in the Laos to the east.

From Muang Fang, a town in the extreme north of Siam, about 20 miles from the border of the Southern Shan States, Wallace Lee

has described sandstones alternating with red Wallace Lee, 1923.

shales, red clays and limy clay shales with a basal conglomerate resting on granite. Fossils collected near Chieng Rai, some 40 miles farther east, were regarded by the United States Geological Survey as of Triassic and probably of Middle Triassic age.

1 Bull. Serv. géol. Indo-Chine, Vol. XIII, Pt. IV, p. 93, (1925). 2 Bull. Geol. Inst. Upsala, Vol. XII, p. 108, (1913-14).

3" Reconnaissance Geological Report of the Districts of Payap and Maharashtra, Northern Siam". State Railways Department, Bangkok, p. 5,(1923).

Wilhelm

or

Wilhelm Credner, however, after his early travels in Siam, concluded that in all probability the folded Red Beds are to be placed

in the younger Mesozoic. He continues as Credner,

follows :-.“ But besides these strongly folded 1930-35.

Red Beds, which represent a continuation of the terrains

rouges of the French geologists in Indo-China, unfolded, horizontal Red Beds are found in the spacious region of the Korat Plateau, which in the north-west of this area, appear to overlie the older, folded rocks discordantly. Hogböm also extended. to these the adoption of a Triassic age, in which, however, we are unable to follow him. These young Red Beds are separated from the older ones by a sharp discordance and between the deposition of the two, the Himalayan folding intervened. The younger group is therefore probably to be placed in

be placed in the Middle Late Tertiary”. It was indeed these conclusions in the case of Siam which confirmed Credner's acceptance of similar ages for the Red Beds of Central Yunnan. B. Hoyböm, however, did not believe that the Himalayan folding affected Siam, for he wrote. “It must be suggested that the Himalayan folding systems have not reached Siam ”2 and, again, “ Cambodia with the neighbouring great Korat Plateau is evidently the massif that has remained longest undisturbed, viz., from the Triassic period”. 3

In a note embodied in Dr. Oskar Weigel's account of the Sapphire Deposits of Bo Ploi, Credner writes of a formation, probably of Mesozoic to Tertiary age, which is wide-spread in Eastern and North Eastern Siam and extends from Indo-China into South China, where it occupies enormous areas in Kwangtung, Kwangsi, Yunnan and Szechuan.4

Credner made several expeditions in Siam and his final views find their expression in a “Systematic Arrangement of the Formation Sequence ” given in his important work on the geography of that country. In this scheme both red formations are placed in the Mesozoic; the upper, unfolded one, distributed mainly on the Korat Plateau, with the proviso “age indeterminable, probably young Mesozoic”; the older, folded group, occurring east of the

1 Milt. Geog. Inst. Sun-Yatsen Univ., Canton, Vol. I, No. 2, p. 52, (1930).
2 Op. cit., p. 108.
3 Op. cit., p. 109.

* Wissenschaftliche Kryebnisse meiner Forschungsreisen in Ostasien, Heft 1, p. 8, (1934).

highlands of Northern Siam and north-west of the Korat Plateau, as probably Triassic. Both formations are stated to be saliferous.

“ The thickness of the beds”, writes Credner, “is very great ; their distribution unusually varying, so that while in Northern Siam they are intensively folded, in the French Laos they lie almost undisturbed. In the Korat Plateau region of Eastern Siam they also rest entirely in even undulations. The deposition of this thick series which was laid down partly before, or during the last epoch of folding and partly after it, appears to have extended over a very long period of time. We know that in the case of South China it reaches from the Trias to the Late Tertiary and an equally long duration for its formation is quite possible in the case of Siam, but it is not yet proved ”.1

Another point in Credner's latest work which has a bearing on his recognition of the view that the Red Beds of Siam are, at least in part of Triassic age, may be mentioned. He states that the limestones which characterise the Trias of the Islands of the Malay Archipelago are wanting in the Peninsula, where the predominantly argillaceous marine deposits of the Malay States form a transition to the terrestial red sandstones which represent it in continental Siam.

Finally, Drs. Arnold Heim and Hirschi surveyed large areas in Siam in 1935. Their results have not been published, but I am

permitted, through the courtesy of Dr. Heim, Drs. Arnold Heim and

to state that the normal succession of strata Hirschi, 1935.

in the meridional ranges of North-Western Siam is the following:

rare

1. Permian limestones with rare Fusulinida, separated by an

unconformity from: 2. Some 1,000 metres of a formation comprising chiefly greenish, siliceous shales, shales, with

pelecypods (Daonella) of Middle Triassic age. 3. Red Beds, commencing with conglomerates, probably of

fresh water origin and containing nodules of limestone. Total thickness over 1,000 metres (3,280 feet).

These Red Beds which are regarded as Upper Triassic to Liassic in age, were found all over Northern and North-Western Siam, as

1“ Siam : das Land der Tai”, pp. 12-13 and 19, (1935).

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