lower bagshot beds. 101 



Lower Bagshot Beds. 



In 1847 Professor Prestwich* pointed out that the series of 

 sands and clays betu-een the London Clay and the OHgocene 

 Beds in the Isle of Wii2;ht is the equivalent of the Bagshot Beds 

 on the mainland. lie also showed that in the Isle of Wight there 

 is a similar three- fold division — into Lower Bagshot, without 

 fossils ; Middle Bagshot, with marine fossils like those found at 

 Braeklesham ; and Barton Clay and Sands, the last two perhaps 

 being equivalent to the Upper Bagshot of the London Basin, 

 perhaps in part (the Barton Clay) dying out northward, or passing 

 into the middle division. 



Subsequent research — especially the observations of the Kev. 

 Osmond Fisher — has added largely to our knowledge of these 

 strata and their fauna ; but there is still considerable doubt as to 

 the exact limits of the divisions, which in fact pass almost 

 imperceptibly into each other. Recent observations have also 

 indicated that the Upper Bagshot Beds in the London Basin are 

 probably the equivalent of the lower part of the Barton Clay in 

 the Hampshire area ; and that the glass-sands (the so-called Upper 

 Bagshot Series of the Isle of Wight) belong to a higher zone, 

 apparently unrepresented north of Hampshire. 



Owing to the Bagshot Beds being nearly everywhere vertical, 

 it has been found impracticable to trace their subdivisions on the 

 map, especially in the absence of fossils. The whole series has 

 thercsfore been grouped together, represented by one colour, and 

 indicated on the map by the letters i 4 to i 7. In this Memoir 

 the term *' Bagshot ' is only applied to the plant-bearing pipe- 

 clays and sands formerly called ' Lower Bagshot.' 



These Lower Bagshot Beds are highly developed in the Isle of 

 Wight, attaining a thickness of 660 feet in Alum Bay. But it 

 may be well at once to point out that part of this great thickness 

 of sparingly fossiliferous beds may be the equivalent of the lower 

 part of the marine Bracklesham Beds, which appear to thicken so 

 greatly towards Whitecliff Bay. 



Lower Bagshot Beds in Alum Bay. 



Ft. In, 



Very thinly laminated pale yellow sand - - - 10 



White crimson, and rose-coloured variegated sand passing 



into pale brownish-yellow sand - - - - 50 



Thinly laminated light grey pipeclay " . " . " ^ ^ 



Pale yellow sand and white laminated clay, with crimson") 

 streaks. I 



Details of the upper part of this subdivision : — Ft. In. 



Yellow sand - - - - 14 6 



Pipeclay parting - - - - — 



White sand - - - - - 11 6 



Yellow sand - - - - 12 



White and crimson sand - - - . 



Uo4 



* Quart. Journ. Geol. Soc, vol. iii. p. 386. 



