Dr. L. F. Spatli — Lower Lias Ammonites from Skjje. 171 



Memoir on " The Geology of Glenelg, Lochalsh, and the South-East 

 Part of Skye " (1910). They are therein referred, as by 

 Professor Judd in his well-known paper on " The Secondary Rocks of 

 Scotland ", to the bucliandi and semicostatus zones. Jadd, the 

 founder of the zone of A. semicostatus, certainly, however, mis- 

 identified some of his Ammonites, besides confusing his Lincolnshire 

 A. geometricus with Young and Bird's A. semicostatus of a much 

 higher horizon. Similarly, the Rev. J. E. Cross, in his paper on the 

 " Geology of North-West Lincolnshire " {Q.J.G.S., vol. xxxi, 1875), 

 recorded A. semicostatus from both the lower Gryphcea i^icurva 

 beds and the higher Scunthorpe Ironstone, which presents close 

 analogy with the gmuendensis-AiJtomoceras-Agassiceras beds of the 

 Harzburg Ironstone. In reality this Ammonite (Arnioceras 

 semicostatum) occurs in a much higher zone than either of these 

 Lincolnshire beds. 



The well-known extended range of "' Arnioceras " and the difficulty 

 of distinguishing the various species of this genus have generally 

 frustrated attempts at a correlation of ^rnioceros-bearing beds in 

 different areas. It may be mentioned here, for example, that 

 Quenstedt, m his " Ammoniten des schwabischen Jura ", figures 

 only one and a very obscure " species " of Arnioceras {A. falcaries 

 olifex) from beds that, in Dorset, can be subdivided into about 

 six subzones. Through the kindness of Dr. W. D. Lang, the writer 

 has been able to study the Ammonite fauna of these 53 feet 

 of ^rniocera.s-bearing strata (Nos. 53-74) at Charmouth, and it is 

 important to note that these beds {Agassiceras and higher zones) are 

 later than any of the Skye strata here dealt with. Apparently, 

 however, even the Dorset forms of Arnioceras, collected by Dr. Lang, 

 do not include examples from the true semicostatus bed. This the 

 writer believes to be in the hirchi subzone, though, as yet, not found 

 in place. The Survey, it may be noted, had placed the whole of these 

 beds 53-74 above the semicostatus zone. It should be added that 

 specimens of Xipheroceras cf. capricornoides (Quenstedt), in the 

 British Museum, have been found attached to two slabs of this 

 Dorset semicostatus bed, and that Professor Blake already noted the 

 occurrence of his A. nigrum, which, like A. flavum and A. 

 anageneticum, S. Buckman, is a constant companion of A. 

 semicostatum, with Am. hirchi. The description of the Dorset material 

 (Part ii, '" Notes on the Ammonites" in Lang, Spath and Richardson : 

 '•■ Shales- with-Beef, a Sequence in the Lower Lias of the Dorset 

 Coast," Proc. Geol. Soc, No. 1,079, January 13, 1922, p. 30) contains 

 the major details of these higher beds, but it will be seen that 

 Judd's ''Zone of A. semicostatus" must be abandoned, for, like 

 Wright's " Zone of Arietites turneri ", it was based on a mis- 

 identification. 



The Broadford Beds here dealt with include the A^tomoceras and 

 gmueiule^isis subzones, with possibly the Upper Coroniceras subzone 

 below, but neither the three lower subzones (bucklandi, rotiforme. 



