﻿82 ME. S. S. BCCKMAN ON CERTAIN [Feb. I9IO, 



Phlyseogrammoceras cf. disjoansum. They date the Lingula Bed as 

 Dumortierice-dispansi hemera, and make it exactly contemporaneous 

 with the middle part of the Gloucestershire Cephalopod Bed, and 

 with the lower 100 feet of the Yeovil Sands near Yeovil. 



Striatuli-spinati (The Junction Bed). — There are two situ- 

 ations in which the Junction Bed of the coast can be studied 

 ■in situ : in the cliffs and on the beach in the fallen blocks. In 

 the cliffs is the best place to lind the striatulus layer ; and, after 

 scraping away some of the overlying clay, portions of this layer 

 can be detached with a chisel, and then broken up for exami- 

 nation. One of the best places for this purpose is on the west side 

 of Doghus Cliffs ; but curiously enough, even in the cliffs, the 

 striatulus layer is often missing. It is always missing, so far as my 

 knowledge goes, from the Junction Bed at Thorncombe Beacon, and 

 it is rarely found in the blocks on the shore : small portions of it 

 may sometimes be found loose on the shore. 



For general examination of the Junction Bed, the shore is the 

 best place ; but, as the blocks are often upside down, care is required 

 in collecting. A heavy hammer and good chisels are also necessary. 



The complete series of the Junction Bed is seldom, perhaps never 

 found. While the striatulus layer, if it be met with, is only found 

 under Down and Doghus Cliffs, the basal Marlstone layer is not 

 present until one is well under Thorncombe Beacon. Even then the 

 upper layer of Marlstone — Day's Pleurotomaria Bed 1 presumably — 

 is often absent. 



Sometimes the greenish rock — the falciferum layer — is absent ; 

 •sometimes it is 10 inches thick, at other times 3 inches. The most 

 persistent rock is the pink rock — the bifrons layer ; there seems to 

 be no failure of this* Its colour reminds one of the colour 6i bifrons- 

 yielding beds of the Toarcian of Lombardy. The pink bed is 

 generally separated from the falciferum layer by an ironstone band 

 1 to 2 inches thick. 



With a little practice it is quite easy to distinguish the different 

 layers when they are lying detached from blocks : roughly there 

 are — the white (striatulus), the pink (bifrons), the greenish 

 {falciferum), and the brown (Marlstone). 



J. F. Blake's suggestion that the Junction Bed was an aggregate 

 deposit formed at one time by the sweepings of various zones ~ fails 

 to meet the facts of the case : there are not only the layers of 

 distinct matrices, but they contain their distinctive fossils, in definite 

 sequence. It is true that there has been erosion and redeposition 

 nearly all the time : thus the Marlstone is conglomeratic, and 

 -contains sometimes Blue Lias pebbles (? algoviani, or lower); 

 the bifrons bed sometimes holds broken and worn specimens of 

 Harpocerata. which really belong to the bed below; while the 



1 Quart. Journ. Geol. Soc. mo\. xix (1863) p. 284. 



2 'Excursion to Bridport, &c.' Proc. Geol. Assoc. toI. xv (1898) p. 295. 



