62 



SCIENCE- GOSSIP. 





GEOLOGY fm 



CONDUCTED BY EDWARD A. MARTIN, P.G.& 



Some Deep London Borings. — Id addition to 

 the borings, particulars of which have already 

 appeared (Science-Gossip, vol. v. p. 118), the fol- 

 lowing have been made by Messrs. C. Isler & Co.. 

 of Bear Lane. Southwark. who have again kindly 

 placed at my disposal the various sections in detail : 



Place of Boring 



Albert Hall Man- 

 sions (Hnssey) 



Aldersgate Street 

 < Manchester 

 Hotel) 



Baa>hot Street. 

 S.E. (White) 



Battersea, Pure 

 Water Co . . . 



Berinondsey - 

 Hornsey Lane 

 ( Barrow) . . . 



Berinondsey — 

 Park Street 

 (Bowrom .... 

 : Bermondsey — 

 Staple Street 

 (Pint) . 



Brewery Road, 

 N. (Crosse & 

 Blackwell).... 



Bromlev-bv-Bow 

 (Three "Mills 

 Distillery,) . . 



Camberwell — 

 Cunard Street 

 (White) 



Camberwell — 

 Neate Street 

 (White) 



Camden Town 

 N.W., Pratt St. 

 (Idris & Co.) 



llOH 







= s 











~- £ 



■s 





.'- — 



*8| 



- 



P - 





- =-i | 



-7- ~ 



_ 



"3 



a to 





c g = 3 | 













"*-■§ 

 *5: 



4 



5 



> T 



| 



■S aO Sffi 



5 3 



3= 



3 '- 



- 



? ■£ s= 





^— 







— 



214 



70 



13 



12?} 



426* 50iX)116 



6 101 

 20| — 



26 142 



28 27 



29 60* 



27 45 



33 23 29 158 350 plen- 127 

 tiful 

 13* 37 289 360 600J 23 



94 35 159 4'JO 4000 43 



21 404 954 250 3000 584 



116 421 



29* 284163 3504 2500 70 



32 24 



300 67S0 78 



32 64 219 450 3500 210 



46 105 25u 27>A' 44 



184 — i-l 10 35 296 362 12000 27 



23 — — 44 36iJ302 366 laree 204 

 SPP.V 



114 73 314 19 16 259J 410f 4320160 



The figures placed in my hands show the thick- 



of the various layers quoted from a litho- 



logical point of view, such as " sand and pebbles " 

 or " blue clay and stones." These I have grouped 

 together under the names of the usually accepted 

 tertiary formations, according as their composition 

 seemed to agree most closely with those formations 

 as seen elsewhere. It will, however, at once be 

 understood that the grouping of the thicknesses 

 assigned to such beds as the Oldhavens and 

 Thanets may be subject to correction. The rise of 

 the Chalk in the south-east of London is clearly 

 brought out by this table, the Camberwell borings 

 showing small tertiary thicknesses over the Chalk. 

 Any material found which may represent the 

 basement -bed of the London Clay has been included 

 with that formation. At Messrs. Barrow's. Hornsey 

 Lane. Bermondsey, 1 foot of "pebbles" was met 



with ; at Messrs. Bowron's, in Park Street, likewise 

 in Bermondsey. there were H feet of " dead sand 

 and pebbles.*' In the "Woolwich Beds the word 

 "rock" appears occasionally; there were 6 feet 

 at Albert Hall Mansions. At the Pure "Water 

 Company "s well in Battersea there was § foot of 

 •• stone " ; at Hornsey Lane. Bermondsey. there 

 were 2^ feet of " very hard rock." Included in the 

 Chalk in the Hornsey Lane section is a layer of 

 h foot of " green-coated flints "" at the top of the 

 Chalk. — Edward A. Martin. 



Correlation of River Terraces. — One of 

 the most puzzling branches of " drift " geology is 

 that relating to the correlation of the various 

 groups of rocks which make up the Pleistocene 

 system. In dealing with widely separated areas 

 we are satisfied if we can say that two deposits are 

 homotasial, and as a general rale we make no 

 attempt at arriving at a chronological classifica- 

 tion of the deposits. One of the exceptions to 

 this rule I propose to discuss is the chronological 

 classification of the river-drifts of the Thames 

 Valley. In this case, as every geologist knows. 

 the factor usually taken is the surface level of the 

 ten-aces or groups, to which the deposits in ques- 

 tion are referable ; those occupying the higher 

 elevations being the older chronologically, and those 

 occupying the lower elevations being the newer. 

 So far as any individual district of narrow dimen- 

 sions is concerned, this plan works admirably : 

 but when we come to compare the strata of one 

 district of the valley with those developed in 

 another portion, we find that the surface levels 

 which have proved such trustworthy allies in the 

 former case begin to break down when applied to 

 a large area ; hence we become exceedingly con- 

 fused in our comparisons. The reasons for this 

 failure are numerous, and the variations spring 

 from a variety of causes, some of which we will 

 briefly consider. In the first place, it is obvious 

 that the surface level of a patch is constantly 

 changing through the agency of meteorological 

 phenomena, inasmuch as the surface level coin- 

 cides with the contour. Further it is obvious that 

 such changes are not carried on to an equal extent 

 over even restricted areas, for in dealing with such 

 deposits as the gravels and brick-earths, we are 

 dealing with deposits which exhibit ever-changing 

 lithok gical characters. At one point we may find 

 an extremely coarse gravel, and a few yards 

 further the same beds are seen to pass into a com- 

 paratively fine sand. Again, in one place the beds 

 may be firmly compacted by ferric hydrate, in 

 aiKther immediately at hand they may be quite 

 loose and incoherent in texture. Another agent of 

 variation may be found in the erosive power of per- 

 colating water acting on the strata upon which 

 the Pleistocene deposits repose. It is sufficient 

 to merely refer to this, at this point, as a fuller 

 consideration of it and an interesting sidelight 

 which it throws will be given in the sequel. 

 H we admit, as I think we must, that the surface 

 levels are essentially unreliable when taken over 

 large areas, it follows that some other character 

 has to be discovered to serve as our principal factor 

 in the case. This cause. I venture to state, will 

 be found in the mean level of the surface of each 

 of the platforms upon which the Pleistocene strata 

 of the different terraces repose. It will be seen 

 that, with certain variations which are hereinafter 

 described, this "basal level"' is remarkably con- 

 stant for each terrace. It may be objected that 



