Geology. 5 



may be found underneath them, but if they are of Old Red Sand- 

 stone (or Devonian) age, the Coal Measures (if they were ever 

 there) have now been eroded away, as the whole of the great 

 Carboniferous Series (of which the Coal Measures form the upper 

 part) comes in between the New Red and the Old Red. It may be 

 well to give some account of this important controversy, as it has 

 a local as well as a general interest, Crossness being one out of the 

 four borings in the London Basin in which these debatable red rocks 

 were found. Sir J. Prestwich (who believed the Kentish Town 

 Red Beds to be Old Red, and we may take those of Crossness as 

 being of the same age) says : " The value of the . . . determina- 

 tion [of Devonian rocks] consists in the fact that in the range of 

 the Carboniferous series through Belgium and the north of France 

 they are everywhere accompanied, on the same strike, by Devonian 

 strata, and the latter strata are constantly brought by great faults 

 and flexures into juxtaposition with the Coal Measures." (i) 



In the " Guide to the Geology of London " (2) it is stated " that 

 there is a strong reason against the classification of the bottom 

 beds at Kentish Town and Crossness with the Old Red Sandstone, 

 which seems to have escaped notice. Having the series unmis- 

 takably present in the Devonian type at Cheshunt and at Meux's 

 [Tottenham Court Road], it would be strange indeed were it to 

 occur in its wholly distinct Old Red type at Kentish Town, between 

 these two places, and at Crossness, not very many miles from the 

 latter of them ! ... no such thing is known to occur anywhere ; 

 the two types of what is generally taken to be one great geological 

 system being limited to separate districts, and not occurring 

 together." 



Prof. Judd, in 1884, in a paper dealing with the Jurassic Deposits 

 under London, principally based upon the Richmond boring, says : 

 " the possibly high angle of dip of these strata [Red rocks] . . . 

 may appear, at first sight, to afford an argument in favour of the 

 Palaeozoic age of the rocks. ... On the other hand, the presence 

 of disseminated particles of galena, and the considerable proportion 

 of chloride of sodium in the water obtained from these Red rocks 

 at Richmond, are obvious points of analogy with the Triassic 

 strata." (3) This dip may, however, be that of current-bedding, 

 and not of regular bedding. 



Prof. Hughes, in the discussion on the above paper, raised a 

 difficulty as to assigning a Triassic age to the red beds, namely, 

 that " nowhere else did an unconformity so marked occur between 



(1) Quart. Journ. Geol Soc., 1878, Vol. XXXIV. 



(2) 1880, Ed. 3, p. 21. Repeated in Ed. 4, 1884. 



(3) Quart. Journ. Geol. Soc., Vol. XL., p. 751. 



