﻿Yol. 66.~] CERTAIN JURASSIC STRATA OP SOUTH DORSET. 67 



distinct beds for the geologist. The upper or Terebratula Bed may 

 be recognized by its whitish colour, the masses of Terebratula 

 ' sphceroidalis," and the excellent preservation of its numerous 

 bluish-coloured Parkinsonian : this is the truellii zone. At the 

 base are some few inches of an ironshot layer, the Astarte Bed, so 

 called from the abundance of Astarte (now Crassinella) obliqua; 

 though the species, or something very similar, also occurs in the 

 bed above. 



This Astarte Bed, or ironshot marly bed, contains fine specimens of 

 Garantiana, of ParTcinsonia rarecostata, and of forms intermediate 

 between that and P. parkinsoni. It is Hudleston's P.l, and can be 

 dated exactly as Garantiana Beds. It is of the age of the Bubbly 

 Beds and Building- Stone of Sherborne in North Dorset. 1 



Below the Astarte Bed is a massive bed, known to the workmen 

 as the 4 th Bed, or the Red Bed. It is so massive that, even with 

 the help of a quarry man wielding a sledge-hammer, little impression 

 can be made on the very large blocks lying on the sea-shore. For 

 this reason, and because it is not richly fossiliferous like the other 

 beds, it has not been possible to obtain information as to the exact 

 sequence of fossils in the bed. All the available evidence points to 

 the bed being a conglomerate, containing the fossils of various 

 dates mixed in more or less confusion. The latest date, indicated 

 by a PerisphincteSy is the niortensis hemera : hence it may be 

 surmised that the deposition of the bed, or of the greater part of 

 it, was finished in that hemera ; but right at the top are found 

 Stepheocerata of the blagdeni and sauzei hemera?, with a matrix 

 agreeing more with the middle part of the bed. 



In the bottom 9 inches of the bed are large limonitic concretions, 

 sometimes measuring as much as 4 inches in length by about 

 3 inches across. They are arranged roughly in two layers, and are 

 known to the workmen by the expressive name of Snuff-boxes. 

 These snuff-boxes are also found about 3 miles to the north, inland, 

 in quarries near the high road about 2 miles east of Bridport. 



The matrix associated with the snuff-boxes at Burton is coarsely 

 ironshot, different in character from the rest of the bed above. 

 From the workmen and from scattered blocks have been obtained 

 specimens showing somewhat this character of matrix — Witchettice 

 and alticarinate Sonninice of the 8. propinqiians tj^pe — species of 

 the Witchelliaz and sauzei hemera?. 



The conclusions that may be drawn concerning the date or 

 dates of the deposition of the Bed Bed — including the snuff-box 

 layers — are: — that the bed was begun in the Witchellice or sauzei 

 hemera, was continued during the blagdeni hemera, and was much 

 disturbed, broken up, and greatly re-arranged during the niortensis 

 hemera. 



This Red Bed affords a good instance of the difference between 

 zones and hemera?. It cannot be said to belong to any definite 

 zone or zones : rather is it a mix-up of several zones ; but it is 



1 Quart. Journ. Geol. Soc. vol. xlix (1893) p. 507. 



p2 



