8 J. BUCKMAN ON THE CEPHALOPODA-BEDS OF 



Here then we have designedly tabulated about sixty species of 

 Cephalopoda from D'Orbigny's ' Paleontologie Francaise, Terrains 

 Jurassiques,' as this author has referred fully one quarter of the 

 species to the Lias. It is an extraordinary list (even though not 

 yet fully made out) for about two feet of rock. 



If we inquire how it is that so many of the species have been 

 allocated to the Lias, we shall find that some few of them have un- 

 doubtedly ascended upwards from the lower stratum ; but most of 

 them have been called Liassic upon the assumption that our Brad- 

 ford Cephalopoda-bed and our sands were the equivalents of those 

 beds in Gloucestershire, and both supposed of Lias age. This we 

 know, not only from references by D'Orbigny himself, but also from 

 having seen fossils from my own quarry of the age of the Gryphite 

 Grit labelled as from " the Upper Lias." 



From all this it appears evident that while some English geolo- 

 gists have confounded two beds fully 100 feet apart, and made their 

 lists of fossils harmonize with this view, both some foreign and home 

 savans (taking, be it observed, these two beds to be one) have, in 

 the same way, made them to harmonize with the Upper Lias of the 

 Continent. 



Now I have not had the pleasure of a personal examination of 

 foreign oolites, but I can plainly see that they have been interro- 

 gated to support theories no less than have those at home ; and I 

 can well believe that if they at all harmonize with our Dorset strata, 

 foreigners, like ourselves, may have confounded two beds widely 

 apart. 



That they do so harmonize we are strongly inclined to believe 

 from D'Orbigny's drawings of Cephalopoda, as in Dorset we have 

 not only a large number of species referred for the first time to our 

 home rocks, but they are for the most part in a fine state of preser- 

 vation — so much so, that the terminations of the Ammonites have in 

 many cases been clearly made out. 



It may be further remarked upon this list of Cephalopods, that 

 although the bed in which they occur has been made out over a 

 wide district, and in all cases it preserves its peculiar character, yet 

 it differs at various points as to the prevalence of species. 



Thus at Bradford Abbas the Ammonites subradiatus prevails. At 

 Babylon Hill the A. Murchisonce is more common, while midway 

 the A. Sowerbii takes the lead. At Halfway House the A. Parhin- 

 soni is the characteristic fossil for a part of the quarry, and the A. 

 subradiatus for another part. Further to the east, at Sherborne, the 

 A. Hum^liresianus assumes importance ; whilst at Clatcombe, a mile 

 from there, the A. Braikenridgii is not only a common but a most 

 perfect fossil. 



Now if it be assumed that this Cephalopoda-bed at these different 

 points occupies a different horizon, of course we can recognize them 

 as different zones, and name them after their prevailing Ammonites ; 

 but it is not so ; and it is a remarkable fact that from 2 to 3 feet of 

 the oolite rock in a limited area should present not only so great a 

 crowd of inrliyiduals but such a variation in species. 



