half of the boundary of the plains. To the south, in contact with
the gneiss and sub-metamorphics is a great volcanic outburst of trap,
which is stratified, and is brought to the surface with the general
rise of elevation along the face of the hills between Shella and
Theriaghat south of Cherrapunji. This has been described as the "Sylhet
trap." South of the main axis of this metamorphic and volcanic mass are
to be found strata of two well defined series: (1) the cretaceous,
and (2) nummulitic. The cretaceous contains several important
coalfields. The nummulitic series, which overlies the cretaceous,
attains a thickness of 900 feet in the Theria river, consisting of
alternating strata of compact limestones and sandstones. It is at
the exposure of these rocks on their downward dip from the edge of
the plateau that are situated the extensive limestone quarries of
the Khasi Hills. There are numerous limestone caves and underground
water-courses on the southern face of the hills. This series contains
coal-beds, e.g. the Cherrafield and that at Lakadong in the Jaintia
Hills. Some description of the remarkable Kyllang Rock may not be out
of place. Sir Joseph Hooker describes it as a dome of red granite,
5,400 feet above sea level, accessible from the north and east, but
almost perpendicular to the southward where the slope is 80° for 600
feet. The elevation is said by Hooker to be 400 feet above the mean
level of the surrounding ridges and 700 feet above the bottom of
the valleys. The south or steepest side is encumbered with enormous
detached blocks, while the north is clothed with forests containing
red tree-rhododendrons and oaks. Hooker says that on its skirts grows
a "white bushy rhododendron" which he found nowhere else. There is,
however, a specimen of it now in the Shillong Lake garden. Numerous
orchids are to be found in the Kyllang wood, notably a beautiful white
one, called by the Khasis _u'tiw kyllang synrai_, which blooms in the
autumn. The view from the top of the rock is very extensive, especially