138 PROF. J. W. JFDD ON THE OLIGOCENE 



deposits of sand and gravel almost everywhere conceal the under- 

 lying Tertiaries from our view. 



Although additions to our knowledge of the fauna and flora of 

 these beds have been made by the examination of such isolated ex- 

 posures as are to be found in railway-cuttings, brick-pits, quarries, • 

 and wells, yet, in seeking to determine the relations of the several 

 beds to one another, we are obliged to fall back upon the more ex- 

 tensive and continuous sections exhibited in the sea-cliffs ; and it is 

 a fortunate circumstance that these coast-sections are both numerous 

 and well exposed. 



It may be readily believed, too, that the frequent repetition of beds 

 deposited under similar conditions, and therefore presenting identical 

 mineral characters, will be a fruitful source of error, unless the aid of 

 the palaeontologist be constantly invoked to enable us to identify the 

 several members of the formation by their organic remains. And 

 the geologist must be prepared to avail himself to the fuUest extent 

 of the researches of investigators of strata of equivalent age in other 

 areas, where important light may be thrown upon the order of ap- 

 pearance of the forms of organic life which occur in our own district. 



In my study of these strata, which has occupied me during many 

 years, I have endeavoured to avail myself, as far as possible, of 

 these different kinds of assistance. Moreover, in my examination 

 of the positions and relations of the strata, I have been greatly aided 

 by the publication of the admirable 6-inch and SS-inch maps of the 

 Ordnance Survey, which supply us with the means of plotting the 

 cliff-sections in a manner which was not possible at the time when 

 the geological survey of the island was made, when no Ordnance 

 map existed, except the obsolete and incorrect 1-inckmap of 1810. 

 I will now briefly enumerate the conclusions to which I have been 

 led by these studies. 



The strata exposed at the base of Headon Hill, at the western 

 extremity of the Isle of Wight, are not, as supposed by previous 

 observers, a mere repetition, through an anticlinal fold, of the beds 

 seen in Colwell and Totland Bays, but are on a distinct and lower 

 horizon than the latter. These Headon-Hill beds are also found to 

 contain a different assemblage of fossils from that which charac- 

 terizes the Colwell- and Totland-Bay beds. I shall show that this 

 new reading of the succession of strata in the Hampshire basin 

 harmonizes much better with the order established by foreign geo- 

 logists and palasontologists than does the one usually accepted. 

 Indeed it will be made apparent, as the result of this investigation, 

 that the sequence of beds in this country agrees most closely with 

 that of the equivalent Middle Tertiary strata in France, Belgium, 

 and Northern Germany. Finally, it will be proved that the thick- 

 ness and importance of this series of strata is much greater than 

 has hitherto been supposed, attaining to not less than 800 or 900 

 feet ; and it will be shown to belong to the lower division of a great 

 system of strata, which is represented, both in Europe and North 

 America, by deposits of enormous thickness, everywhere charac- 

 terized by large and distinctive faunas and floras. 



