ON THE BAGbHOT EEDS 0¥ THE LONDON BASIN. 415 



e. Besides these pebble-beds, large very irregular masses of pebbles 

 occur occasionally in the Middle and Lower Bagshot Beds at or 

 near the surface, possibly more or less reconstructed. 



2. The Upper Bar/sliot Sands contain few, if any, clay bands, are 

 not, as a rule, false-bedded, and have a great abundance of irony 

 concretions, which often either are, or contain, casts of marine 

 shells. 



3. The Middle Bagshot Series is characterized by green sands and 

 clays. The former frequently contain Bracklesham shells, and they 

 do not lose their green colour by weathering, even when exposed 

 for a considerable length of time, as, for instance, at Goldsworthy 

 HiU. 



4. The Lower Bagshot Beds are, as a rule, false-bedded. They 

 frequently contain seams of pipe-clay, and sometimes thicker beds 

 of clay occur. There are numerous irony concretions ; but, unlike 

 the Upper Bagshot, marine shells are rarely, if ever, found, though 

 wood is common. They never when exposed contain dark green- 

 sand beds, though beds of green sand attributed to this series have 

 been described in well-sections. 



With regard to the fossils which are found in the Bagshot beds, 

 Mr. Irving makes the following observations, which we think require 

 explanation. He says (Quart. Journ. Geol. Soc. vol. xli. p. 508) 

 " this is borne out by the numerous casts of diminutive forms of a 

 saltwater fauna which are met with in the buff-yellow sands of the 

 Upper Bagshot, at horizons not far above the pebble-bed at the 

 base," and (same page) "The difficulty in the way of the theory 

 suggested in this paper arising from the presence of marine shells, 

 (e. g. at Yateley) in the Middle Bagshot beds, may be perhaps 

 removed if we recollect that (1) they occur very locally ; (2) they 

 are, as a rule, much broken, worn, and even comminuted ; (3) 

 they appear to be confined to the coarser sediments of the Middle 

 Bagshot beds." 



In our experience the Upper Bagshot fossils are of the size usual 

 in Barton beds, and not confined to any particular horizon, but the 

 best-preserved specimens are found high up in the series. 



The Middle Bagshot fossils are usually present wherever the green- 

 sand bed occurs ; they are not, as a rule, broken or comminuted, 

 but entire, the valves of the bivalves being generally united, and 

 any breakage that may be apparent being the result of pressure after 

 deposition. 



Now, if geologists, adopting the theory of Mr. Irving, assign 

 much of what has hitherto been recognized as Lower Bagshot to 

 the Upper Division, they will have to deny the truth of many of 

 these conclusions, which, in the face of the evidence which we have 

 brought forward, we do not think they will feel themselves war- 

 ranted in doing. They will have to account for the absence of 

 green sand where it ought to occur, for the presence of false- 

 bedding and pipe- clay where we should not expect to find them, 

 and for the absence of fossils at horizons at which they may usually 

 be discovered. They have also to account for the peculiar ground- 



