170 Geological Society : — 



as the alleged 'Eolithic' working; finally it was stained, marked 

 with glacial striae, and covered with a thin layer of white silica. 



This implement appears to prove that Palaeolithic man lived on 

 the Kentish plateau before or during the deposit of the plateau- 

 gravels, and that the ' Eolithic ' chipping is not the work of man. 



2. ' On the Grouping of some Divisions of Jurassic Time.' By 

 S. S. Buckman, Esq., E.G.S. 



The author argues for an arrangement in the division of Jurassic 

 time based upon the zoological phenomena of the Ammonite-fauna. 

 He considers that such time-divisions should be related to the duration 

 of Ammonite-families. He divides the Jurassic Period into two 

 epochs — the Eojurassic and the Xeojurassic : the former the time 

 when the Ammonite-families of the Arietidae and their close ally 

 the Hildoceratidae were dominant ; the latter commencing just upon 

 the extinction of these families, and being the time when the 

 Stepheoceratidae held chief sway. 



The epochs are subdivided into ages, and the ages again are 

 divided into hemerae — a hemera being the chronological unit. 

 Reasons are given for the different subdivisions, and for commencing 

 the Eojurassic Period with the rotifonnis-hemem. 



The Eojurassic Period it is proposed to divide into four ages — the 

 Sinemurian, the Pliensbachian, the Toarcian, and the Aalenian. 



During the Sinemurian age, whereof the zoological phenomenon 

 is the acme and paracme of the Arietidae, was deposited a part of 

 the Lower Lias, beginning w T ith the zone of Amm.omtes Bucllandi and 

 ending with that oL4. oxynotus. This age is divided into the following 

 seven hemerae, stated in ascending order: — rotiformis, gmuendensis, 

 Birclii, Turneri, obtusi, stellaris, oxynoti. 



During the Pliensbachian age, marked by the dominance of 

 Deroceratidae and Amaltheidae, was laid down the rest of the 

 Lower and almost all the Middle Lias. It includes seven hemerae, 

 namely: — raricostati, armati, Jamesoni, Valdani, striati, margaritati, 

 sjpinati. 



During the Toarcian age, when the Dumortierice and a part of 

 the Hildoceratidae were prominent, the following strata accu- 

 mulated : — a small part of the Middle and the whole of the Upper 

 Lias, the Cotteswold Sands, the Midford Sands, and a portion of the 

 Yeovil Sands. There are ten hemerae : — acuti, fahiferi, bifronlis, 

 Lillice, variabilis, striatuli, Struckmanni, dispansi, Dumortierice, 

 Moorei. 



During the Aalenian age, when there was a preponderance of 

 another portion of the Hildoceratidae which may be known as the 

 Liidivigia-gTOu^, and of Hammatoceras, the rest of the Yeovil 

 Sands and a part of the Inferior Oolite were the accumulated 

 deposits. This age is divided into the following six hemerae : — 

 naleasis, opaliniformis, scissi, MurcJiisonce, bradfordensis, concavi. 



Part of the Neojurassic division is separated into two ages. 

 During the first, the zoological phenomenon is the acme and 

 paracme of Sonninince ; during the second, the predominance of 

 Parlinsonia?. 



