118 /. AitJcen — On Faults in Drift. 



and at others scattered about singly in the sand or gravel. The over- 

 lying beds, having an aggregate thickness of about 11 feet, are com- 

 posed of brown and mottled clay, sand, and gravel. Kunning along 

 the lines of bedding and faults are thin layers of argillaceous sand, 

 about half or three-quarters of an inch in thickness, which, on account 

 of possessing a greater power of resistance to sub-aerial degradation 

 than the principal body of the sand, give a degree of sharpness and 

 distinctness to the section but rarely witnessed in strata of this 

 character. It is further noteworthy that the faults do not extend 

 through the whole vertical depth of the exposed strata, but are con- 

 fined to about 9 feet in thickness of the subordinate beds, the bed 

 No. 8 presenting the appearance of arching, or curving, over the 

 elevated conical portion near the centre of the section, as though 

 that division had been forcibly thrust upwards, and partially forced 

 into the overlying bed at a time when it had only recently been 

 deposited, and when, for want of pressure, it had not become suffi- 

 ciently consolidated to fracture like the rest, but was from that 

 cause in a plastic and yielding state. The supposition that the 

 superincumbent beds of clay, sand, and gravel were deposited at a 

 period subsequent to the dislocation of the subordinate strata, not 

 only fixes the time of its occurrence, but also accounts for the 

 perfectly undisturbed character of these upper beds. 



Most of the Drift faults described in the Geological Magazine 

 occur in strata resting upon the Cretaceous formation, and it has, 

 with some degree of probability, been suggested that, at least in 

 some of the instances mentioned, the appearance of faulting may 

 have resulted from subsidence of the superior beds into caverns, 

 or hollows, produced in the calcareous beds beneath by the me- 

 chanical force of running water, or the chemical action of the acids 

 contained therein. This suggestion, although worthy of the fullest 

 and most favourable consideration, in those instances where the 

 Drift immediately reposes upon chalk or other calcareous rock, 

 easily operated upon by the agents referred to, loses its force when 

 applied to those of an arenaceous character like those at Stockport, 

 which, as is well known, are almost destitute of all calcareous in- 

 gredients in their composition. 



Whether the dislocations here encountered extend to and also 

 affect the subordinate Triassic rocks, it is impossible to say, as they 

 are concealed from view by other and lower members of the Drift 

 formation ; but, if we may judge from analogy, no reasonable doubt 

 can exist that such is the fact ; indeed it is difficult, if not impossible, 

 to conceive of any other way in which they can have been produced, 

 under the circumstances here stated, than by a sympathetic action 

 with the underlying rocks. 



"Whilst writing upon the subject of faults in Drift, I may be per- 

 mitted to refer to the description of a section of this character given 

 by Professor Hull, at p. 182, Vol IV. of this Magazine, which was 

 exposed to view during the progress of the work in preparing the 

 site for the New Town Hall at Kochdale ; the origin of which 



