﻿354 A. J. Jukes Browne — On the Tipper Greensand, etc. 



and were, I believe, the first to point out the threefold division 

 of the Upper Greensand as developed in Hampshire and Surrey. 

 They say : " It commonly comprises three distinctive formations ; 

 the first is a thin green band of marl, more or less siliceous, and 

 abounding in organized fossil remains ; it lies below and in contact 

 with the soft dirty white marl above mentioned ; in thickness it varies 

 from a few inches to 10 or 15 feet. The second division is the fire- 

 stone rock, the thickness of which also varies. . . . This rock 

 gradually merges into a soft clayey marl, which constitutes the 

 third sub-division, and this again in its inferior parts becomes more 

 and more argillaceous, until it is finally lost in the Gault." Mr. 

 Godwin- Austen, writing in the same year, makes a similar division 

 of the series near Guildford,^ but refers the lowest green marls and 

 clays containing phosphatic nodules to the Gault. 



Here, again, there is no definite base-line for the Upper Green- 

 sand, and certain clayey marls are referred by one observer to the 

 Gault and by others to the Greensand ; it will be seen in the sequel 

 that I look upon the former mode of grouping as the most correct. 



In 1862 two memoirs were published by the Geological Survey 

 describing the Isle of Wight and parts of Hampshire and Berkshire 

 (Sheet 12) ; no detailed sections of the Gault and Greensand are 

 given in either of these works, but the following may be deduced 

 from the description on p. 24 of Mr. Bristow's " Isle of Wight," and 

 may be compared with those on a previous page. 



Feet 



1. Calcareous Sandstone 20 



2. Chert, Sandstone, and Freestone ? 16 



3. Sands and Sandstones , ?24 



4. Yellowish-grey sand with some Sandstone and Chert (? fiag) ... 40 



5. Bluish sandy micaceous beds 55 



155 



It is to be regretted that the fossils found in these beds were not 

 given separately instead of being combined into a general list. 



As regards the base-line, Mr. Bristow says (p. 23) : " Sometimes 

 the Gault assumes a very sandy character, and passes so insensibly 

 into the Upper Greensand as to be scarcely distinguishable from it." 

 A section also is given showing the passage from Gault to Greensand, 

 and the bluish sandy claj'S are stated to contain Gryphcea vermicularia 

 and Area; the line is mainly drawn to separate sands from clays, 

 the sandy clays being mostly included with the Upper Greensand, 

 and not with the Gault (see ante). 



In the Memoir on Sheet 12 the Upper Greensand is described as 

 consisting of the same three divisions previously indicated by Messrs. 

 Paine and Way, viz. (1) Greensands ; (2) Malm rock ; (3) Soft 

 sandy marls ; but the former of these is referred to the Chloritic 

 Marl, leaving the other two only to constitute the Upper Greensand. 



Thus we find that there is great uncertainty both concerning tlie 

 upper and lower limits of the formation, and that the only beds 

 which all agree in calling Upper Greensand are the Malm-rock and 



^ Quart. Journ. Geol. Soc. vol. iv. p. 257. 



