By A. J. Jukes-Browne, B.A., F.G.8. 



335 



are not agreed as to the line of demarcation between the two. 



Even if we follow Professor de Lapparent, who makes the Albien 

 include the zone of Ammonites inflatus, we could not adopt that 

 name for an English group which also includes the zone of Pecten 

 asper, because all the French geologists agree in regarding this zone 

 as an essential part of the Cenomanien. On the other hand, we 

 could not exclude the zone of P. asper because it is an essential part 

 of our Upper Greensand, and it would be impossible to draw a 

 continuous line of division in the midst of a mass of soft sands. 



Hence we are driven to conclude that the only satisfactory solution 

 of the difficulty is the introduction of a new name for the group of 

 beds which lie between the Vectian and the horizon known as the 

 Chloritic Marl. I have considered all the places situate on the 

 Gault and Greensand in the south of England, but have not suc- 

 ceeded in finding any town, river, or district, which affords so 

 appropriate a name as Devisian. The fact is that the tracts occupied 

 by the outcrop of these strata were in British and Roman times 

 covered with such thick woods and were so full of springs and 

 quagmires that they were unsuited for the establishment of towns or 

 military stations and were for the most part wild and uninhabited 

 districts like Selwood Forest. From this fact Sylvanian has been 

 suggested as a name, but as most other argillaceous outcrops were 

 equally sylvanian it is not sufficiently distinctive, and it lacks the 

 definite association with a typical district which is embodied in 

 Devisian. 



My object in discussing this question has been to make it plain 

 that the use of the old names Gault and Upper Greensand only 

 serves to perpetuate error ; it is not merely a fancy on my part that 

 such a name as Devisian or Sylvanian will look prettier and be more 

 convenient, but it is absolutely necessary if our names are to signify 

 definite portions of geological time that a new name should be found 

 for that portion of time during which the Gault and Upper Green- 

 sand were formed. I wish it to be understood that I am not now 

 proposing any special name ; I have simply discussed the names 

 that seem to me to be available, and if any of my readers can suggest 

 a better name I shall be very willing to consider its merits. 



