RAJMEHAL GROUP. 61 



Other similarly measured sections might be quoted, but the above 

 are sufficient to illustrate the character of the lateral distribution of the 

 trap and the interbedded shales. 



From many measurements it would seem that the ordinary flows 

 of basalt range in thickness between 70 and 350 feet. But flows much 

 less than 70 feet do occur, and frequently there are hills of trap of from 

 500 to 700 feet thick in which no break, caused by an inter trappean 

 bed, is apparent. 



" The trap rocks vary in character from a very fine grained, hard and tough 

 basaltic rock, ringing clearly under the hammer, and fracturing with edges as sharp 

 as in flint, to a comparatively soft and largely crystalline or even earthy rock 

 generally containing large quantities of olivine. Amygdaloidal trap is also very 

 abundant, the majority of the cavities being filled with various forms of quartz, 

 agate or chalcedony. Stilbite, more rarely natrolite and analcime in small transparent 

 crystals, also occur. These agates and zeolites are most abundant in the beds or flows 

 of trap which underlie the white and whitish shales (viz., Nos. 5 and 7 of general 

 section). The uppermost trap is never amygdaloidal. It is a thick mass of glassy, 

 compact basalt, in places not less than 1,000 feet in thickness. Below this, where the 

 alternations of trap and sedimentary deposits occur, the traps still continue to be 

 tbe prominent feature in the hills. They are of much greater thickness than the 

 shales or bands interbedded with them ; the latter vary from 2 or 3 feet up to 

 about 40 feet, while the interposed sheets of trappean rocks are from 30 to 100 

 feet in thickness. However, in this thickness, as in all other characters, there is much 

 irregularity. Each flow of trap sometimes appears to be of X)ne mass, or again seems 

 to consist of two or more flows, often well marked by differences in mineral character, 

 composition or texture. 



The section above given exhibits the sequence of the beds only as it occurs in the 

 northern part of the hills, and even there much local variation is seen. Mucb of this, 

 however, may be only apparent and due to the decomposition of some of the traps 

 leaving large exfoliating boulders and numerous angular pieces detached, which, by 

 falling down, always obscure and sometimes entirely conceal the sedimentary rocks 

 beneath. Slips also, as might be expected, are exceedingly numerous, being caused by 

 the soft clays, sometimes associated with the shales and sandstones, yielding under the 

 enormous pressure of the trap above. Thus the whole of the more level ground in 

 the Moorcha (or Mujwa) Pass is almost covered by a confused intermixture of traps 

 and shales. This at first conveys the idea of a country cut up by innumerable faults, 

 but is unquestionably due to enormous slips ; immense masses having subsided from 

 the adjoining hills into the valley. 



( 215 ) 



