RED CRAG. 461 



increased the list of fossils, and have discovered remains of 

 Tunicata {Lepioclmtwi tcnuc), and spicules of Calcisponges. They 

 conclude that the deposit was accumulated during the earlier 

 portion of the Red Crag period, but Mr. Clement Reid is disposed 

 to group it with the Lenham Beds, which are of the age of the 

 lower part of the Coralline Crag.^ Possibly the St. Erth beds may 

 represent passage-beds between these strata. 



Messrs. Kendall and Bell are of opinion that during the accumu- 

 lation of the St. Erth Beds no channel of direct communication 

 existed between the North Sea and the Atlantic Ocean, the Straits 

 of Dover being closed, while on the north-west the Tertiary 

 volcanic chain threw a barrier across from the north of Scotland 

 to Greenland by way of the Shetland and Faroe Islands and Iceland. 

 Such a barrier may have had considerable influence on the climate 

 of later Pliocene and Glacial times in North Britain. Deposits 

 of sand and clay, apparently similar to those of St. Erth, occur at 

 St. Agnes Beacon, but they have yielded no organic remains." 



RED CRAG. 



This deposit consists generally of dark red shelly sand, exhibit- 

 ing false-bedding, and having a thickness of from 25 to 40 feet. 

 Sometimes the colour is yellow, brown or grey. Seams of 

 laminated clay are occasionally met with. 



Mr. S. V. Wood, jun., expressed the opinion that the lower stages of the 

 formation were not, as a rule, deposited under water ; but from their being 

 regularly inclined at angles varying between 25*^ and 35°, he regarded them as due 

 to a process of ' beaching up,' by which was formed a reef extending from the 

 river Aide on the north to the southern extremity of the deposit in Essex. At 

 Walton-on-Naze, however, the lowest bed of grey Crag contains evidence of 

 being a subaqueous deposit, and is remarkably free from derivative fossils ; but it 

 is covered by two reef stages, and these again by horizontal beds. The uppermost 

 beds are generally horizontal, and contain evidence of having been formed under 

 water. Owing, however, to the probable reconstruction or re-accumulation of 

 different stages, Mr. Wood considered it impossible to separate the Red Crag in 

 general into more than three divisions, as follows : ■^ — 



c, 1 • 1 ■ ,^ ( Largely made up of TeUina fira-tenttis, and T. 



■X. hcrobiculana Crag. < f, -' -.t, 1 c / • / ■ >i/ 1 2-^ j \ 



•^ ^ ( cH>Lqi<a, \\\\.x\ ^iVio ScniLuciilana pla)ia ypipcrata). 



2. Deben, Orwell, and Butley Red Crag, with northern forms of mollusca 



predominating. 

 I. Walton Grey and Red Crag, containing many species characteristic of the 



Coralline Crag. 



' Nature, Aug. 12, 1886, p. 34.2. 



^ W. A. E. Ussher, Post-Tertiary Geology of Cornwall, 1879, p. 12 ; G. Mag. 

 1879, p. 103 : De la Beche, Report on Geol. of Cornwall, etc. p. 258. 



•* Q. J. G. S. XX. 121, Ann. Nat. Hist. (3), xiii. 185. See also Prestwich, 

 Q. J. xxvii. 324, 352 ; T. G. Ringler-Thomson, Q. J. v. 353 ; W. Whitaker, 

 Geology of Ipswich, etc. (Geol. Surv.), p. 29. 



