Chap. VIII.] trap dykes and intrusions. 145 



There is no reason for supposing that the trap outbursts of Central 

 India and the Deccan ever extended to the neighborhood of Bengal, 

 unless they were contemporaneous with the traps of the Rajmahal Hills, 

 a view opposed to the opinions entertained by all Indian geologists ; 

 the Deccan traps being considered Eocene. It is, therefore, highly 

 improbable that the dykes of the Raniganj field should be in any way 

 connected with them. And the balance of probabilities appears to 

 be in favor of those dykes being of Rajmahal age. 



It is remarkable, considering that both dykes and faults must neces- 



„ ,, . sarily take place alone; lines of weakness — along 



Faults accompanying •> L ° ° 



d y kes - cracks in the rock, in fact — that instances of their 



accompanying each other should be so singularly rare in the Damuda 

 Valley. Only two cases were observed. Of these one is the dyke 

 (No. 6 of Mr. Williams*) which runs nearly due North and South 

 along the valley "West of Sirsol, and passes just West of the out-crop 

 of the Sirsol coal seam; the other is on the North boundary of the 

 field, just East of the Barakar. A fault runs North-west from near 

 Debipur to the temple at Debitan. The Southern portion of this is 

 accompanied by a trap dyke, which, however, is clearly more recent 

 than the fault, for the latter is cut off close to Debipur by a second 

 fault, running about East 20° North, while the dyke is continued for 

 some distance without being thrown. Doubtless other cases may 

 exist of faults and dykes being along the same lines, but had 

 tbey been other than extremely scarce and exceptional, more in- 

 stances would certainly have been noticed. It is evident that the 

 disturbing forces producing pressure on the beds, and tending 'to 

 crack them, at the time when the traps were intruded, were dis- 

 tinct from those existing in the previous period of dislocation and 

 disturbance. 



* The dykes marked on Mr. Williams's map were all numbered, but, as before stated, they 

 were a very small portion of those which existed. 



T 



