I'AttT II.] 
.57 
Blanford: Geology of Orissa. 
1. M’ETAMOBrnic on Crystalline Rocks. 
These consist of various forms of gneiss, mica-schist, hornblende-schist, quartzite, &c. 
Crystalline limestone, common in many parts of India, has not been hitherto observed in 
Orissa. True granito occurs in the form of veins traversing the gneiss, and is of various 
forms, the most common being a highly crystalline variety with but little mica, and passing 
into Pegmatite of the hind known as graphic granite, beautiful specimens of which havo 
been found in parts of the Tributary Mahals. This granite is apparently, for the most part, 
at least of contemporaneous age with the metamorphism of the gneiss. But, besides this, 
the gneiss itself frequently passes into a granitoid form perfectly undistinguishable in blocks 
from granito, but which, when in place, is usually found to retain every here and thero 
traces of its original lamination, and to pass by insensible degrees into a distinctly laminated 
gneiss of the usual form. 
Other prevalent forms are ordinary gneiss composed of quartz, felspar, and mica; horn- 
blendic gneiss in which the mica is replaced by hornblende; the lattor mineral sometimes 
forming a very large proportion of the rock, and quartzoso gneiss, in which the felspar 
and mica or hornblende, are in very small proportion and tho quartz predominates. This 
gradually passes into quartzite: a massive rock in general, in which felspar and mica aro 
either wanting or occur only in very small quantities. 
The above may be considered the prevailing forms of the crystalline rocks; hut there 
aro others of less frequent occurrence. Amongst these are diorite, amphibolite, syenite and 
a magnesian rock, a kind of pot-stone occasionally resembling sei'pentine. These may all, 
very possibly, be of later date than tho mass of the metamorphics, though the serpentine-like 
pot-stone appears to be fairly intercalated. 
2. Talchib Gbotjp. 
The lowest beds associated with the coal-bearing strata are themselves destitute of 
useful fuel, and well distinguished mineralogically from the Damuda or coal-bearing rocks. 
They were first separated from the overlying beds in Orissa, and were named after the estate 
in which they were found. They consist, in the Talchir Coal Field, of blue nodular shale, 
fine buff or greenish sandstone, and of extremely fine silt beds, often interstratified with sand¬ 
stone more or less coarse in texture, in thin alternating laminae. The sandstones often 
contain felspar grains which are usually undecomposed. In the sandstone and fine silty 
shale, rounded pebbles and boulders of granite, gneiss, and other crystalline rocks frequently 
abound, some of them as much as four or five feet in diameter. This remarkable formation 
is known as the ‘boulder bed,’ it is peculiar to the Talchir group, and has been found in India 
wherever that group has been examined; in tho valleys of tho Damuda, the Sone, tho 
Narbadda, and the Godavari, as well as in that of tho Bramini. 
Of this singular association of largo blocks of stone in a fine matrix, but few other 
instances are known, the most remarkable one being that of the ‘ boulder clay’ ol Great 
Britain and other countries, which is now by most geologists considered to be of glacial 
origin. Thu boulder bed of the Talchir group differs entirely from the boulder clay 
however; in the former, tho fine matrix is distinctly stratified, and tho boulders are rounded, 
neither of which is tho usual condition of tho boulder clay. But tho origin of such a rock 
is, in both instances, surrounded by the same difficulty, viz, that any current of water which 
could round and transport tho boulders would sweep away, instead of depositing, the fine 
sand, clay, and silt in which they are imbedded. Yet nothing is clearer thau that the two 
were deposited together. loo is rather a startling power to invoke in endeavoring to 
