Geological Society of London. 327 



Formation. — The term Formation shall be applied to a smaller 

 group of rocks which have some lithological or palgeontological 

 character in common, but which may be in continuous sequence 

 with the rocks above and those below. 



Deposit. — Deposit was defined as a term applicable to a smaller 

 division than Formation, and generall}'^ implying similarity of litho- 

 logical character. 



Zone, Hohizon. — Zone was defined to be part of a Formation 

 characterized by one or more well-marked species, and Horizon was 

 allowed to be correctly used for such part of a Formation, when it is 

 recognized elsewhere by other characters, though the fossils may be 

 absent. 



It was agreed that Bed, Group, Series, should be left undefined. 

 Some other terms still remain under discussion. 



Concerning Time- words, it was agreed that Period should be used 

 for the largest division, and should signify a completed and well- 

 defined portion of time. Age was defined as a term used to indicate 

 tlie ]3ortion of time marked by the prevalence of certain forms of 

 life or of similar material having a distinct and well-marked 

 character. Epoch was defined to mean a point of time, an interval 

 short in comparison with the Periods and Ages of which it forms a 

 part. It was considered that it could hardly be applied to the whole 

 duration of even any one form of life, though it might to the transi- 

 tory appearance of a species for a short time in one area. CycJe and 

 Date were left undefined, and the definition of Era was postponed. 



Geological Society of London. 



I— May 11, 1881.— Eobert Etheridge, Esq., F.E.S., President, in 

 the Chair. — The following communications were read : — > 



1. "Notes on the Fish-remains of the Bone-bed at Aust, near 

 Bristol, with the Description of some new Genera and Species." By 

 James W. Davis, Esq., F.S.A., F.G.S. 



The fossil fishes described in this paper are from the Ehsetic bed 

 at Aust Passage. The stratum containing the fish-remains is rarely 

 more than nine inches thick, often considerably less, and is composed 

 of rounded masses of hardened clay or marl, which, at the time of 

 their deposition, were soft enough to receive the impressions of the 

 coprolites and fish-remains. There are large numbers of coprolites 

 and bones of fishes, as well as some remains of Saurians, mingled 

 with each other indiscriminately. The fishes belong to the orders 

 Plagiostomi and Ganoidei, some of the former being of considerable 

 size. It is inferred, from the intermixture of Saurians and fishes, 

 that the deposit is the result of shallow water existing near laud, 

 in which the fishes lived and the Saurians occasionally disported 

 themselves. 



Besides the fossil remains of the animals which lived during the 

 deposition of the Aust-beds, there are also others which appear to 

 have been derived from the Mountain Limestone and the Coal- 

 measures, representing such genera as Psammodus,Psephodus, Relodus, 



