LOWER LIAS OF ROBIN HOOD'S BAY 



115 



of the geology of parts of the bay were published by Howarth ( 1 955), 

 Phelps ( 1985) and Hesselbo & Jenkyns (1995). The tables of Figs 19 

 and 20 give bed-by-bed correlation columns for all these schemes in 

 as much detail as is possible; the columns of subzones in both figures 

 are the subzones as determined in this paper. 



Simpson first described the beds in 1 868 (Simpson, 1 868: 53-56), 

 but in his later work (Simpson, 1884: xvii-xxii) there are more 

 details at some horizons, and the Simpson columns in the tables are 

 based on his later work. Tate & Blake (1876: 63-65, 73-75, 79-81, 

 91, 92, 109, 1 10) described the beds in greater detail, and in many 

 parts of the succession their beds correspond closely with those in 

 the present paper, though they omitted about 3 m of strata within 

 their group Jam.30-Jam.32. Tate & Blake (1876: 79, 91-2) also 

 duplicated part of the succession in their descriptions, inasmuch as 

 their Jamesoni beds 1-7 are the same as their Capricornus beds 28- 

 33 (these are shown in Fig. 19 as Jam.l-Jam.7 only). 



The Geological Survey's description of the succession first 

 appeared in the memoir of Fox-Strang ways & Barrow (1882: 4-10), 

 where the beds were described in detail but not numbered, and the 

 ammonites that they listed for individual beds are not accurately 

 determinable in modern terms. The same description was used by 

 Buckman (1915: 67-74) in his appendix to the 2 nd edition of that 

 memoir: the same basic data was used for the succession, but the 

 beds were sometimes combined into thicker units and were now 

 given numbers; lithological names were given to a few of the beds, 

 and Buckman's determinations of the ammonites and zonal divi- 

 sions were added. Buckman's 1915 description of the sequence is 

 used for Figs 19 and 20, rather than the original 1882 description. 



Howarth (1955: 155) described beds upwards from the bottom of 

 the Upper Pliensbachian; the equivalence of his beds 1-6 are shown 

 at the top of Fig. 19, with bed 1 being the same as beds 600.5 and 

 600.6, while the equivalence of a few lower beds that were given 

 roman numbering in the upper part of the Figulinum Subzone is 

 indicated in the detailed stratigraphical section above (p. 98). 



Phelps (1985: fig. 4) described the succession in the Davoei and 

 upper part of the Ibex Zones in detail. When the vertical tabular 

 section of his fig. 4 is compared at the same scale with the tabular 

 section of Fig. 18 here, good correlations can be made from his top 

 bed near the top of the Figulinum Subzone down to his bed 4b (= bed 

 567) in the Masseanum Subzone, and at the bottom it seems fairly 

 certain that his bed 1 is the same as bed 561. Phelps (1985: pi. 1, figs 

 1, 3, pi. 2, figs 1, 6, 8) figured five ammonites from his beds 21, 23, 

 37, 47 and 63, the identifications of which are discussed below 

 (pp. 141-144) in the description of the ammonite genus Aegoceras. 



Hesselbo & Jenkyns's (1995) sequence of the Lower Lias of 

 Robin Hood's Bay was based on new observations made by them. 

 Their bed numbers are original from the bottom of the sequence up 

 to their bed 1 2 1 at the base of the Masseanum Subzone, then higher 

 up they used the bed numbers of Phelps (1985), and finally the bed 

 numbers of Howarth (1955) upwards from the top of the Figulinum 

 Subzone. Although their descriptions and measurements were new, 

 above bed 1 2 1 their identification and use of Phelps ' bed numbers is 

 difficult to interpret at some horizons, especially in the Ibex Zone, so 

 in Fig. 19 the correlation of Phelps' beds 1-65 is based on Phelps' 

 original description of that sequence, not on Hesselbo & Jenkyns' re- 

 interpretation of it. However, from the base of the sequence up to bed 

 121, Hesselbo & Jenkyn's description can be readily correlated with 

 that of this paper at most levels, and is shown as their beds 1-121 in 

 the relevant columns of Figs 19 and 20. The main areas of uncer- 

 tainty are at the bottom of the succession below their bed 23 (=bed 

 447), though it appears likely that their bed 5 has been correctly 

 identified as bed 422 (Low Balk), in their beds 73-94 in the Taylori 

 Subzone, that are difficult to correlate in detail, and in beds 113-121 



in the Brevispina and Jamesoni Subzones. In the upper part of the 

 sequence between beds 102 and 1 16, a strikingly similar pattern can 

 be seen by comparing Hesselbo & Jenkyns' tabular section side-by- 

 side with that ofFig. 17;eg. bed 102 = bed527; 104 = 531; 1 12 = 543; 

 1 14, lower part = 545, and it is probable that bed 1 16 is the same as 

 bed 547. Bed 1 of Phelps has already been correlated with bed 561, 

 so this leaves Hesselbo & Jenkyns' beds 117-121 (4.5 m thick) as 

 eqivalent to Bairstow beds 548-560 (6.3 m thick), but there are some 

 differences in thickness and they are not correlatable in detail. The 

 position of the subzone boundaries given by both Phelps and Hesselbo 

 & Jenkyns differ in detail from those determined for this paper, 

 except for the upper parts of the Raricostatum and Davoei Zones. 



In addition to the previous descriptions in the works listed above, 

 Getty measured and collected ammonites from the Oxynotum and 

 Raricostatum Zones in the bay. The stratigraphical part of his work 

 is only available in his unpublished thesis (Getty, 1972), but many of 

 the ammonites he collected were described in his revision of the 

 family Echioceratidae (Getty, 1973), and they are in the collections 

 of the Natural History Museum. His stratigraphical sequence of 

 ammonites and biostratigraphical divisions are very similar to those 

 of Bairstow as determined here. 



BAIRSTOW'S AMMONITE COLLECTION 



More than 2360 ammonites were collected by Bairstow. The major- 

 ity were obtained in the years 1927-1935, but small numbers of 

 specimens were added up to about 1970. In addition there are a few 

 specimens that were given to him by other collectors: the majority 

 came from Dr J. Coggin Brown, who collected well-preserved 

 ammonites at Robin Hood's Bay in the period 1940-1960 (on 

 retiring to north-east England after working for the Geological 

 Survey of India). Bairstow checked the horizons of the specimens 

 given to him with great care, and only those that he was satisfied 

 came from definitely identifiable beds are included amongst those 

 listed in this paper. All Bairstow's ammonites are preserved in 

 collections of the Department of Palaeontology, The Natural History 

 Museum, London, and most have been given Museum registration 

 numbers, in addition to the collecting numbers given by Bairstow. 

 The identifiable Liparoceratidae were registered for Spath's (1938) 

 catalogue of that family, and received some of the numbers in the 

 series C.38871-C. 39579; some of the Eoderoceratidae were regis- 

 tered in the late 1950s in the series C.493 14-C.4943 1 ; the remainder 

 of the collection was registered in 2000 with the numbers CA 2744- 

 CA 4608. The three nautiloids in his collection have the numbers CN 

 86, 87 and 93. 



In 1928 Bairstow consulted with S.S. Buckman, a year or two 

 before his death, who had expressed interest in the ammonites he was 

 collecting in the bay. From his earlier work on ammonites collected 

 by the Geological Survey, Buckman knew that the succession up to 

 the top of the Sinemurian was exposed in both the north-western and 

 south-eastern parts of the bay. The sequences of ammonites that 

 Bairstow was obtaining in the two outcrops that are up to 3 km apart 

 seemed to Buckman to be a good opportunity to test his hemeral 

 theory 1 , and he advised Bairstow to record the geographical position, 



'Briefly, Buckman's theory of hemera was that every species of ammonite reached its 

 acme of abundance at a unique time that did not overlap with the acme of any other 

 species. By discovering the order in which ammonites reached their acme, a sequence 

 of 'hemerae' could be constructed, which would be smaller and finer divisions than 

 ammonite subzones and would be applicable over wide areas. Contemporary palaeon- 

 tologists were sceptical of the theory, and work by many palaeontologists during the 

 following 70 years has shown that the hemeral theory is not valid. 



