262 DR. H. HICKS ON THE MOKTE SLATES, AND [May 1 896, 



IV. MlTLLACOTT, SheLFIN, AND ILFRACOMBE. 



The discovery by me in 1891 of a fairly rich fauna in a quarry 

 on Mullacott Farm, having a strong Silurian facies, led rae to make 

 a careful examination of the boundary-line between the Morte Series 

 and the Ilfracom.be Beds in this area, and to note any special changes 

 visible in the beds near the junction. During this examination it 

 soon became apparent that there was no gradual passage between 

 the Ilfracombe Beds and the Morte Slates, as had previously been 

 maintained to be the case, but that there was everywhere an 

 important petrological difference to be noticed, which could only be 

 the result of beds of very different age being brought into contact 

 either by a fault or an unconformity. To enable me to make out 

 what was really the cause of this abrupt change, I found it necessary 

 to trace with care the Ilfracombe Beds to the north in coast-sections 

 and in the valleys about Ilfracombe, and evidence was soon obtained 

 to show that where beds had been indicated as dipping regularly to 

 the south, and hence under the Morte Slates, they as often dipped in 

 the opposite direction, that they were bent into a series of acute folds, 

 and that the strong cleavage had often been mistaken for bedding- 

 planes. After this it became possible to follow certain well-marked 

 beds through the various folds, and to make out that these rose up 

 higher and higher in the sections as we approached the Morte 

 States, and indicated the southern edge of a well-marked trough, as 

 shown in fig. 2. Further examination revealed the fact that there 

 was marked evidence of much crushing where the Ilfracombe Beds 

 were in contact with the Morte Slates, and therefore that the line 

 of separation here, at least, was an important thrust-fault. 



Much of the evidence, so far as it relates to the Ilfracombe Beds, 

 has already been given by me in a paper in the Geol. Mag. for 1893, 

 therefore it is only necessary now to refer to that portion of the 

 evidence which more particularly explains the nature of the junction 

 between the Ilfracombe and Morte Beds. The Ilfracombe Beds are 

 often much broken by faults and frequently inverted, but there are 

 well-marked petrological and palseontological horizons which enable 

 the beds, even when most disturbed, to be identified : therefore, 

 though beds at different horizons are occasionally brought into 

 contact with the Morte Slates, the line of junction, when these facts 

 are borne in mind, can be, as a rule, easily traced. 



In Mullacott Hill there is very little superficially to mark the 

 fault-line, but just above Score, in a quarry worked for road- 

 metal, some massive sandstone-beds of the Ilfracombe Series, though 

 in a greatly crushed condition, are seen dipping away from the 

 Morte Beds. North of Great Shelfin the fault runs along a narrow 

 valley, the hill on the northern side being formed by the basal sand- 

 stones of the Ilfracombe Series, and that on the southern side by the 

 Morte Beds. In an easterly direction the fault crosses the Oakridge, 

 and afterwards extends through the valley which runs nearly east 

 and west, north of Bowden. 



The sandstones of the Ilfracombe Beds remind one much more 



