64 INFERIOR OOLITE AMMONITES. 



ascending order the full sequence of strata should be — 1, Murchisonse-zone ; 2, Concavum-beda ; 3, 

 so-called Sowerbyi-zone. When we consider with what attention the Inferior Oolite has been studied 

 upon the Continent we cannot fail to be surprised that so many new species of Ammonites should be met 

 with in our English strata, most of which species occur in the Concavum-beda. Mr. Hudleston has 

 noticed the same fact concerning the Gasteropoda. Not only so, but it seems to me that the species 

 of Ammonites from these beds which are already named are practically absent from the Murchisonse- 

 or Sowerbyi-zonea of the Continent. But this fits in exactly with a theory which supposes the 

 Concavicm-beda to be intermediate between the continental Murchisonse- and Sowerbyi-zones, and to 

 be absent on the Continent ; and it seems to me that the number of new species can be explained in 

 no other way. It might be suggested that the Concav um-beda form part of tbe Murchisonse-zone • 

 but the Ammonite- and Brachiopod-Fauna. of the two horizons in Dorset are perfectly distinct and 

 always characteristic, whilst of those Continental species which do occur in the Concavum-beda the 

 majority belong to the so-called Sowerbyi- rather than the Murchisonse-zone. 



Dr. Vacek (' Oolithe Cap San Vigilio ') has noticed that a great hiatus exists between the 

 Murchisonse- and Sowerbyi-zones of the Continent both geologically and palseontologically, and he has 

 therefore proposed that this point was the most natural at which to draw the line of demarcation 

 between the Lias and Inferior-Oolite formations. On account of the extraordinary and truly oolitic 

 development of the former zone in the Cotteswold area — so different to what appears to be the case 

 on the Continent — this proposition cannot fail to be most unmeaning to English geologists ; yet it 

 must not therefore be summarily dismissed. At present it appears to me that the strata, of which 

 the Bradford-Abbas quarry is the type, supply, in the form of the Concavum-beda, that "missing 

 link " whose absence M. Vacek has detected upon the Continent. 



Between the Maliere and the typical Bajocian of Normandy (I get my information from Mr. 

 Hudleston, ' Gasteropoda,' p. 27, Pal. Soc, vol. xl) is an extremely well-marked break. Evidently this 

 is the break to which Vacek refers, and which he finds to be persistent over a large area. The 

 question whether the Concavum-beda are intermediate between and really connect the Maliere and the 

 Bajocian cannot be definitely decided until I have figured all the species which occur in them and 

 comparisons can be made with the Continental Eauna. If the majority do not occur in either the 

 Murchisonse- or Sowerbyi-zonea of the Continent, or if only certain recognisable mutations of these 

 species occur, then it appears to me that this theory concerning the Concavum-beda will be tenable. 



In the Stroud area the strata show a marked hiatus between the Upper Ereestone and the 

 Gryphite-grit — the Lower Trigonia-grit of the North Cotteswolds is absent. In the North Cotteswolds 

 the hiatus occurs between the Gryphite-grit and Upper Trigonia-grit (Parkinsoni-zone) — the strata 

 which were being deposited during this interval {Humphriesianum-zone, &c.) being found at Dundry 

 and in Dorset. (This same hiatus occurs in the Stroud area, but not marked stratigraphically as in 

 the North Cotteswolds.) At Bradford Abbas, I am unaware of any hiatus, although the strata 

 between the Concavum-beda and the Parkinsoni-zone are much attenuated. Although the recom- 

 mencement of deposition was different in the two cases, yet the hiatus in Normandy begins evidently 

 on about the same horizon as the marked one in the Stroud area ; but for that very reason is 

 different to that of the North-Cotteswold hiatus. It is probable that the Concavum-beda were being 

 deposited in Dorset during the interval thus represented ; this must actually have occurred under 

 similar circumstances in the Cotteswolds. 



I have no wish to create a new zone. The Concavum-beda will, perhaps, have to be merged into 

 the Murchisonse- or so-called Sowerbyi-zone for convenience' sake even if their intermediate character, 

 so far as the Continental zones are concerned, be recognised. At present it seems better — especially 

 considering the doubtful position of Am. Sowerbyi as revealed to me by recent investigations (see next 

 note) — to treat the Concavum-beda as a distinct horizon. 



