346 JURASSIC. 



These remains are abundant both in Dorsetshire and in the Vale of 

 Wardour.^ 



The Purbeck Beds, as a rule, rest conformably upon the Portland strata, 

 although local symptoms of unconformity have been observed.^ They were 

 included with the Wealden Beds by Fitton and Mantell,-* and as part of the 

 Purbeck-Wealden Series by Topley ^ (1875) ; but they were first grouped with the 

 Oolitic series on the suggestion of Edward Forbes.^ 



The beds pass upwards, as Mr. H. W. Bristow has shown, into the variegated 

 Wealden Strata. This is well exhibited in the section at Mewps Bay, east of 

 Luhvorth Cove, on the Dorsetshire coast, which is generally regarded as the most 

 complete section of the Purbeck strata. The junction-beds are as follows : — 



ft. in. 



,,, ,, T, 1 \ White siliceous sand with lignite )„ ^ 



Wealden Beds, j j.^^^ ^^^^ ^^^^ ^^^^^^ ^^^^^ ^^^_ j 7 o 



/ Purple green and grey Marls with Paludina II O 



I Paludina Marble O 6 



Upper Purbeck! Red and green Marls with /'a///fl'/«a 4 o 



Beds. j Paludina Marble O 9 



f Grey clay with Paludina 2 7 



V Paludina Marble 6in. to i O 



The Purbeck strata may be regarded as passage-beds between the Portland and 

 Wealden series, for no rigid boundary-lines mark their limits. Indeed it has 

 been considered that the northerly portions of the Purbeck Beds were to some 

 extent contemporaneous with the Portland Beds further south. ^ 



It has been questioned whether the Purbeck and Portland Beds 

 ever extended far beyond their present limits ; '' but the Wealden 

 and Purbeck Beds, as remarked by Sir A. Ramsay, represent the 

 delta and lagoon deposits of an immense river, which in size may 

 have rivalled the Ganges or the Mississippi. 



The highly inclined and contorted strata at Luhvorth form in- 

 teresting subjects for study. At Stair Hole or Cove the sea has 

 forced its way inland by three tunnels through Portland rocks, 

 perhaps originally joints and fissures ; and this process indicates 

 the probable way in which Luhvorth Cove and Worbarrow Bay 

 were formed. The ' Broken Beds ' noticed by Mr. Bristow along 

 the coast are remarkable. On Portland such beds may in most 

 cases be clearly traced to the "gullies" in the Portland rocks, 

 but this explanation is quite inadequate to explain the disturbance 

 of the beds along the Isle of Purbeck. The effects of weathering 

 along the inclined edges of the strata may have had some in- 

 fluence, and there may have been some crushing of the beds during 

 the great disturbances to which they have been subjected, when 

 the Chalk and other strata of Dorsetshire and Hampshire were 



1 Brodie, Fossil Insects, 1845, Q.J. x. 475 ; H. Goss, P. Geol. Assoc, vi. 116. 



2 J. F. Blake, Q. J. xxxvi. 204. 



3 Isle of Wight, ed. 3, p. 42 (table). See also Dr. C. Struckmann, G. Mag. 

 1881, p. 556. 



* Geology of tlie Weald (map). 

 5 Rep. Brit. Assoc. 1850. 



« Godwin-Austen, Q. J. vi. 47S ; see also Blake, Q. J. xli. 330, 352 ; Phillips, 

 Geol. Oxford, p. 410. 



' J. Morris, G. Mag. 1867, p. 462 ; Judd, Q. J. xxvii. 222. 



