1922 



CHRONOLOGY 



19 



t 



lies the Armorican axis of N. France. Movements of these west to east 

 axes divided the English Jurassic sea at times into areas with and without 

 autochthonous Ammonites. When and where Ammonites are not 

 autochthonous they drifted in, into a closely land-locked area, from 

 the autochthonous district off West Scotland ; when Ammonites were 

 presumably autochthonous all over England there was free communica- 

 tion both N. cmd S. of the island made of Ireland, Wales, Lyonessc 

 and Brittany (Juroceltia), so that the sea joined up West Scotland 

 with the southern autochthonous area — the Paris Basin. 

 The following appears to give the history 



Ages 

 Gigantitan 



I 

 Macrocephalitan 



Clydoniceratan 

 Oxyceritan 



Tulitan 



Conditions 

 Autochthonous Ammonites 

 England. 



all over 



GraciHsphincteaii ^ 



Late Zigzagiceratan J 



Early Zigzagiceratan^ 

 Parkinsonian J 



Stepheoceratan 



I 

 Ludwigian 



Canavarinan 



I 

 Caloceratan 



No autochthones in England. Great 

 destruction of strata. Armorican 

 or a more southern axis perhaps 

 divides. 



The N. Devon axis is, perhaps, the 

 dividing line — shutting in the 

 autochthones to the S. of it. 



No autochthones in England. 

 Armorican axis perhaps the 

 dividing line. 



The North Devon axis divides. 



Autochthones were to the S. of 

 it ; but there would also seem to 

 have been an extension of the 

 Malvemian axis to the Dorset 

 Coast, so that autochthones lie 

 mainly to the west of such a line. 

 See also remarks on distribution 

 of " Fossil Beds " in the Author's 

 paper, Bajocian of the Sherborne 

 District; Q.J.G.S. XLIX, 1893, 

 P- 507- 



The Mendip axis divides in the main, 

 but it was breached between 

 Somerset and S. Wales, so that 

 Dundry had autochthones like 

 Dorset. Dundry was cut off from 

 the non-autochthonous area of the 

 Cotteswolds by an elevation of 

 the Malvemian axis. 



Autochthonous all over England. 



Numbering the west -east axes from S. to N., i, Armorican, 

 2, N. Devon, 3, Mendip, it will be seen that the rhythm of movement 

 presumably is 3, 2, i, 2, i. 



Criteria used in estimating autochthonous areas from those which 



