﻿Vol. 66, .] JTJKASSIC STRATA OF SOUTH DORSET. 89 



Yeovil Sands, the main mass of the Bridport Sands, and the Midf brd 

 Sands in a strict sense, being post-striatulan would be, therefore, 

 Yeovilian. Owing to a non-sequence in the Yeovil district, the 

 finish of the Yeovil Sands coincides with the end of the Yeovilian, 

 which makes the name appropriate ; but, there being a due sequence 

 in the Bridport area, the upper part of the Bridport Sands is later 

 than Yeovilian : it is Aalenian. 



VI. Summary. 



(1) Descriptions are given of certain strata (Lower Bathonian 

 to Pliensbachian) on the Dorset coast — Chideock and Burton 

 Bradstock. 



(2) Comparison is made with similar strata inland — with a 

 summary of beds at Stoke Knap ; with certain Xorth Dorset strata ; 

 and with Toarcian beds of Yorkshire and Northamptonshire. 



(3) The strata described are classified according to what may be 

 called the multizonal or polyhemeral system — in the main, according 

 to the scheme introduced for these strata in 1893 * ; but further 

 divisions due to other investigators and to myself are dealt with. 



(4) The strata described are arranged among thirty-six zonal 

 (hemeral) divisions — a greater number of divisions than Oppel 

 used in 1856 for all the Jurassic rocks, of which these beds form 

 but a small part. 



(5) The Upper Lias part of the Junction Bed of Down Cliffs, 

 Chideock (Lower or Tpre-striatidus Toarcian), is a very condensed, 

 imperfect epitome in 20 inches of about 180 feet of strata on the 

 Yorkshire coast, and of very much more when allowing for gaps. 



(6) Between the bifrons layer and the striatulus layer of the 

 Junction Bed there is occasionally a 2-inch layer which is all that 

 represents some 250 feet of deposit in the Cotteswolds — so that 

 about 2 feet of Junction Bed was formed while a thickness of some 

 550 feet was being deposited elsewhere. 



(7) The Upper Toarcian (moorei-Dumortierice hemera:) makes a 

 great showing at Burton Bradstock and Down Cliffs as the Down 

 Cliffs Clay and Bridport Sands (pars), the greatest thickness of 

 rocks of these dates in the kingdom. 



(8) The sequence of aalensis strata above moorei beds is demon- 

 strated at Chideock Quarry Hill, in the upper part of the Bridport 

 Sands. 



(9) The Inferior Oolite (Aalenian, Bajocian, Bathonian, pars) 

 strata of Burton and Chideock are not counterparts of one another : 

 they supplement each other to a certain extent ; both are in- 

 complete and much epitomized representations of thicker deposits 

 elsewhere. 



(10) Mr. Beeby Thompson's zonal scheme for the Upper Lias is 

 considered, and a table of Upper Lias zones for future work is 

 presented. 



[For the Discussion, see p. 109.] 



1 Quart. Journ, Geo!. Sue. vol. xlix, p. 481. 



