1850.] DE LA CONDAMINE — DISLOCATIONS AT ELACKHEATH. 44/ 



from it by the presence of imiierfectly rolled flints, which never occur 

 in the tertiary bed. 



Thus we have a distinct line of demarcation between the Lower 

 and Middle Eocene periods, " during which," as Mr. Prestwich has 

 observed, " the water acquired greatly increased transporting power, 

 and after which the London clay was deposited in a more tranquil 

 and perhaps a deeper sea." 



Fig. 4. — Section across Blackheath. 



Horizontal scale 1 inch = 500 yards. Vertical elevation increased three times. 

 Observatory. 



8 ,Si.\4S«W»WW, 



1. Gravel. 



2. London clay. 



3. Pebble bed (No. 6). 



4. Striped sandstone (No. 5) 



5. Shell bed (No. 4). 



6. Mottled clay, green sand and pebbles (No. 3). 



7. Ash-coloured sand and flints (Nos. 1 & 2). 



8. Chalk. 



N.W 



The date of the dislocation of these strata is posterior to that of 

 the partial denudation of the London clay. This will appear by 

 comparing the Map with the Section of the faults at Deptford. Be- 



Fig. 5. — Section of the Lines of Dislocation at Deptford. 



Horizontal scale 1 inch = 120 yards. Vertical elevation increased three times. S.E. 



ii Reconstructed bed. 



g 4 Fault. Faults. 



1. Striped sand and loam (No. 5). 



2. SheUbed (No. 4). 



3. Mottled clay, green sand, and flints (No. 3). 



4. Sandy loam. 



5. Ash-coloured sands (No. 2). 



6. Chalk. 



tween the lines ah, cd Csee Map) there is a nondescript mass, which 

 tallies with none of the neighbouring strata, but which is just what 

 would result from the degradation and mixture of the striped sand. 

 No. 5, and the London clay. I therefore suppose the trough or 

 trench formed by the subsidence, real or comparative, of the original 

 surface between a h and c d (see figs. 5 and 6), to have been filled 

 up by the waste of the adjacent beds ; for had the London clay suf- 

 fered no denudation, it would occupy the space in question : whether 

 or not a remnant of it exists beneath the line of railway, remains to 

 be proved. This supposition is favoured by the indistinct basin-like 

 stratification of the sandy loam between h and d. There are also a 

 few pebbles in it, which may well have been derived from No. 6. I 

 have not however observed any fragments of the shell-bed. 



The line of demarcation at d (see Section, fig. 5) is indistinct, the 

 edge of the fractured bed of sand. No. 2, having of course been soon 

 obliterated by the action of water. It is interesting to observe that 

 at 6, the tough strata of No. 5 bent before they yielded to the tension. 



The intensity of the force by which this dislocation was effected. 



