Rev. J. F. Blake — Aggregate Deposits and Zones. 483 



ammonites in one bed is apparent only, and this they attempt to 

 do by asserting that a careful search will show that these fossils 

 occur in their proper position in different portions even of this 

 single band, the older type being found near the bottom and the 

 younger near the top. Theoretically this might be the case. There 

 is no minimum thickness of a zone except that dependent on the 

 fossils it has to contain to be a zone at all, and even in a uniform 

 bed the fossils might be arranged in parallel layers one over the 

 other in their proper order as ascertained elsewhere. Without being 

 acquainted with the strata of all the world one is not in a position to 

 say that this never actually occurs, but personally I have never seen 

 an instance in which a careful attention 'to the lithology would not 

 enable us to indicate a line of separation, however obscure, between 

 the substance enclosing one fauna and that enclosing another, when 

 both are of the ordinary character of more or less tranquil deposit. 



The beds, however, which are claimed as multizonal, in all the 

 cases which I have noticed, possess a peculiar character which 

 removes them from the usual category of deposits, and which it 

 is the object of this paper to point out. 



The true value of zones is best observed and appreciated in those 

 massive deposits, such as the Lias, the Oxford Clay, and the 

 Chalk, which are disturbed by no episodes, and which do not vary 

 in facies, but whose formation has been continuous through the life- 

 history periods of several fossil species. The fossils in these deposits 

 are found imbedded in what may be called their natural position, 

 that is, they have been buried as they fell to the bottom, or died 

 there, each being covered by subsequent portions of the deposit 

 before their successors were buried above them. All the species 

 that lived and died together lie on one surface in the rock, every 

 portion of which has in fact formed the sea-bottom at successive 

 times. This is well known to fossil collectors, who, finding some 

 desired form in one place, can find others like it by following 

 accurately the line of stratification. In this way every millimetre 

 in the thickness of the rock represents the successive soft sea- 

 bottoms. The multizonal bands are entirely different from this. 

 The fossils in them do not lie in a natural position, but often stand 

 on end ; they are not arranged in horizontal bands, but are con- 

 fusedly mixed together or huddled up in heaps ; arnongst them 

 there are often broken fragments, often of a remanie character, 

 and sometimes of considerable size. Now, according to the theory 

 that considers these multizonal bands as the attenuated representa- 

 tives of massive deposits elsewhere, the deposition here must have 

 been very slow ; but the irregular arrangement, the mixed character of 

 the fossils, and the size of the fragments show that, instead of being 

 very slow, the formation of the deposit must have been very rapid — 

 indeed, tumultuous. The material can only have been brought to its 

 present position by strong currents carrying it along horizontally. 



I propose to assign to deposits having these characters the special 

 term aggregates. Although this is proposed in connection with 

 multizonal bands, and is, indeed, intended to suggest how fossils of 



