494 Messrs. Meyer and Jukes-Browne — 



IV. — Chloritio Mael and Warminster Greensand. 

 By C. J. A. Meyer, F.G.S., and A. J. Jukes-Bkowne, F.G.S. 



IN the year 1878 there was a short controversy between us 

 respecting these beds in the pages of this Magazine. Since 

 that date we have both enlarged our knowledge of the beds at the 

 junction of Chalk and Greensand, and recently we have had an 

 opportunity of meeting at Seaton in Devon, and of examining the 

 "Whitecliff and Beer Head sections together. The result of this 

 and of friendly discussion is that we have both modified our views 

 and have come to an agreement on the most important points 

 about which we differed in 1878. Under these circumstances we 

 think it will save trouble and facilitate future enquiry if we jointly 

 express our present views on the subject so far as we are in 

 agreement. 



1. CMoritic Marl. — As far as we can ascertain, this name was first 

 applied to certain beds at the junction of the Chalk and Greensand 

 in the Isle of Wight.^ It was subsequently adopted by Prof. E. 

 Forbes, for a bed which occupied a similar position in Dorset, and 

 has since been used for any bed lying at the base of the Chalk Marl 

 and containing fossils and green grains. 



It does not follow, however, that the basal part of the Chalk 

 Marl is everywhere of exactly the same age ; there may have been 

 continuous deposition over one part of the sea-floor, 'while a 

 neighbouring part was swept by a strong current. We think this 

 was the case, because in some localities there is a complete passage 

 upwards from Greensand to Chalk, while in others there is a clearly 

 marked break and plane of erosion between them. Where there is 

 a passage the beds with phosphate nodules are probably on the same 

 stratigraphical horizon ; but wherever a break occurs the basement 

 of the Chalk may belong to a higher horizon. 



In the Isle of Wight, in N.E. Dorset, and South Wilts there is 

 either complete passage or very slight signs of erosion ; there is 

 always soft greensand below the bed with phosphatic nodules, and 

 the latter always contains the sponge Stauronema Carteri. 



In the western part of Dorset there is always a break between 

 Greensand and Chalk : the top bed of the Greensand is generally 

 a hard calcareous sandstone ; the nodule bed at the base of the 

 Chalk does not contain Stauronema, but yields Scapliites ceqiialis 

 in abundance, whereas in the Isle of Wight Scapliites only occurs 

 in the Chalk Marl about 20 feet above the base.'^ Consequently 

 we consider that the Scaphites bed of Dorset belongs to a higher 

 stratigraphical horizon than the Stauronema bed of the Isle of 

 Wight. 



Now if the name Chloritic Marl is to be retained — and it seems 

 to die hard — we think it should be restricted to the horizon or 



1 Ibbetson, "Notes on the Strata of the Isle of Wight." 'London, 1849. 8vo. 

 ^ It has been recorded from the Chloritic Marl, but we believe that this is a 

 mistake ; at any rate, the find has never been confirmed. 



