10 
Records of the Geological Survey of India. 
[VOL. II. 
There are deceptive appearances of organic structure, such as, minute concentrically 
laminated globular bodies, in some of the Kuddapaii rocks; the coralloid character of the 
Kurnool limestones; minute CypWs-like bodies in the upper limestones; the dendritrie 
crystallizations of the oxide of manganese in quartzites, limestones, and slates ; and lastly 
the cavities of clay-galls so frequent in the sandstones; but these of course are all referable 
to other than organic origin. 
Geological Sketch of the Shillong Plateau: by 11. B. Medlicott, 
P. G. S., Geol. Survey of India. 
The main features of the geology of the Shillong plateau, on the north-eastern frontier 
of Bengal, have been known for some time: cretaceous, nummnlitic, and younger strata, 
resting horizontally upon metamorphic rocks of various types, at an elevation of 4,000 
to 5,000 feet, and doubtfully related to extensive masses of trappean eruptive rocks. A brief 
opportunity has recently occurred of visiting the hitherto geologically unexplored western 
portion of the plateau in the Garo region; and also of re-examining the central portion, 
in the Khasia district, at a season rotten field work' was possible. A brief abstract of the 
results is here given in anticipation of the more detailed description. 
Eegarding the supra nummulitic rocks, which are very poorly exposed in the central 
region, little fresh information has been gained. From, the sandstone of Nongkalong on 
the western limits of the Khasia district, where it rests upon nummulitic limestone, Cap¬ 
tain Godwin-Austen has made a collection of fossils upon which l)r. Stoliczka remarks that 
“ none of the species, so far as recognizable, appear to be identical with those known from 
the nummulitic beds of the same district.” 
The nummulitic formation presents a total change in the character of the deposits 
from east to west: from being purely sandy and calcareous, they become almost entirely 
argillaceous. 
The doubtful horizon between the nummulitic and cretaceous formations has been 
worked out. The former does not overlap the latter; the northern outliers, so far as known, 
are all of the cretaceous deposits. 
The local order of the cretaceous deposits at Cherrapoonji is described. 
Many of the fossils collected have been identified by Dr. Stoliczka with forms occurring 
in the Ootatoor and Arrialoor groups of the upper cretaceous rocks of South India. In 
the small collection obtained, there were recognisable eleven forms of Cephalopoda, twenty- 
seven of Gastropoda, eleven of Lamellibrauehiata, three of Brachioqmla, and four 
Echinoidea. 
A very extensive formation of stratified eruptive rocks is exposed, unconformably over¬ 
laid by the cretaceous strata and resting in natural junction against a steep face of the 
metamorphic rocks along the south base of the plateau. It is fully 3,000 feet thick. No 
inter-truppean sedimentary rocks, nor any infra-trappean younger than the metamorphics, 
having been found, it is impossible to assign the age of this eruptive formation. It is pro¬ 
posed to call it the Sylhet Trap. 
Totally distinct from this is the Khasia Trap, so massively developed in the interior 
of the hills, associated with the younger metamorphics. It is probably hypo-synchronous 
with these, i. e., introduced (f formed) at the time of their main disturbance and meta- 
morphism. 
The granite occurring, both in large masses and in dykes, through the upper meta¬ 
morphics is younger than the Khasia Trap. 
The separation of the Shillong series (the upper metamorphics) from the Gneissic 
series, is conjectumlly indicated. 
The peculiar position of the plateau, between two great regions of disturbance, and the 
close relation of the stratigraphieal features with the south-eastern of these mountain-regions 
arc discussed as illustrative ot current opinions upon crust-movements. 
