The Meghalaya-Mikir Uplands (25° 05′-2fi 41’N and 89° 47′-93° 36′ E) consisting of the Ga Khasi, Jaintia and the oultlying Mikir and Rengm hills is a tableland which has been detached fromtli Indian Peninsula by the Malda Gap. It is borderedb] the Dhansiri river in the east and the Singimari in the west and covers a total area of about 35,291 sq (400 x 40 km).
Its average height lies between 6111 and 1830 m. The Meghalaya Plateau has indeed chequered evolutionary history of emergence, sum mergence and peneplanation with several phases m erosion, sedimentation, diastrophism, intrusion] movements of land and sea and emissions (R.P Singh, 1968, p.l). It is a fragment of the supa continent of Gondwanaland showing traces of peneplanation ranging from pre-Cambrian to Recent and sub-Recent periods. It was partially submerged by die encroaching sea during the Mesozoic and early Tertiary times and was uplifted slowly from the bed of the sea during the Himalayan orogeny. It also experienced deep fissures during the Upper Jurassic period along its southern flank through which a great volume of lava erupted (Bhattacharya, 1969, p. 18).
The plateau mainly consists of rocks of the pre-Cambrian period like granites, gneisses and granulites. The pre-Tertiary and Tertiary rocks occur above these rocks on die western and southern margins of the plateau.
The plateau presents a polygenetic surface with some defined peneplains at varying altitudes. The western part (the Garo Hills) is an extensively dissected tract of 8,164 sq. km with an average altitude of 600 m or less.
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The Tura Range runs through the centre of Garo hills (Norkek peak 1515 m) which is a typical example of horst between two faults. The Kylas Hill in the east of the Someswari river stands out as an abrupt hog-back mass. The central and eastern part consisting of the Khasi and Jaintia Hills is a true plateau (14,375 km2) with its senile topography and flat skyline.
The Shillong peak (1961 m) is die highest peak of the area. Towards die west of Sliillong die Diengiei range attains a height of 1823 m. The southern part of the plateau called War country is die steepest part of the region. Farther soutii beyond Mylliem there is a vast structural platform built of gently dipping sandstones of Cretaceous age on which stands Cherrapunji.
The Jaintia hills in general have more flat lands dian the Khasi hills. The drainage system of die central and eastern Meghalaya Hows down to the SyUiet plain in the south and the Brahmaputra valley in the north. Important rivers include the Khri, Digaru, Umium (in the north), Kynchiang, Mawpa, Umiew-Umian, Myngot and Myntdu (in the south).
Mikir Hills are detached from the Meghalaya Plateau and are surrounded by plains on diree sides. This area has an average elevation of about 450 m widi general slope towards north. The southern ranges known as the Rengma Hills have an average elevation of 900 m. The area is characterised by radial drainage with Dhansiri and Jumna being the main rivers. The Meghalaya-Mikir region is subdivided into the western, central and the eastern parts.
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The western region is spread over the Garo hills, the central over the Shillong Plateau (Khasi hills) and the eastern over the Jaintia and Mikir hills.