CiRC. No. 74. 



sections of Robin Hood's Bay — is the chief authority ; see also the 

 Geological Survey Memoirs, Baker's ' North Yorkshire,' Phillips' 

 'Geology of the Yorkshire Coast,' and 'The Yorkshire Oolites' (Proc. 

 Geol. Assoc, Vol. iii. No. 7). 



Physical Geography and Geology. 



Mr. Hudleston writes the following : — 



This district affords a favourable opportunity for the study of 

 portions of the Lias and Inferior Oolite. Many of the zones of the 

 Lower Lias are well displayed in the scars which are uncovered at low 

 vi^ater, and which are more or less conformable to the general curve 

 of the Bay. The Peak forms the South ' Cheek ' of the Bay. 

 According to the mapping of the Geological Survey the effect of the 

 Peak fault on these scars is to throw the beds of the zones of Am. 

 armatus and Am. oxy?iotns against the viargaritatuS'ht6.% of the Middle 

 Lias, which latter constitute a projecting tongue of rock enclosed 

 within a fork of the fault. The froritispiece to Young and Bird's 

 ' Geological Survey of the Yorkshire Coast ' represents ' a view of 

 the remarkable break in the strata at Peak' as seen from this pro- 

 jecting tongue of rock, which may be said to separate Robin Hood's 

 Bay from Blue Wyke Bay. 



In the cliff itself the effect of this great fault is to bring the Middle 

 Lias into juxtaposition with the Lower Estuarine Series of the Inferior 

 Oolite, the beds on the downthrow side curving towards it, but 

 ultimately assuming a strong dip in the opposite direction, i.e., S,E. 

 Peak Hill, which has an elevation of about 600 feet, is in a great 

 measure the result of this fine stratigraphical feature. It thus possesses 

 a certain resemblance to Scarborough Castle Hill, whose northern 

 precipice is due to a fault having a similar direction. But in the case 

 of the Castle Hill a cross fault has helped to wedge out the entire mass 

 from the adjacent country, which is not so at the Peak. In each case 

 the hill is on the downthrow side, but the removal of the upthrow 

 side at the Peak has been less complete than at Scarborough. The 

 throw of the Peak fault is about 400 feet. 



The summit cutting of the railway does not show a section of the 

 fault, but its effects are seen on the downthrow side by the strong 

 curve in the beds of the Middle Estuarine, whilst a short distance towards 

 the north, the ' alum shale,' or cornnnmis-heds are observed in the 

 next cutting. An interesting section in the old alum quarry close by 

 (Crag Hall) displays the ' alum shale,' surmounted by the Dogger, 

 here 07ily four feet thick, which is succeeded by the Lower Shale and 

 Sandstone (Lower Estuarine). A peculiar feature in connection with 

 the development of the Jurassic rocks of this district is the attenuation 

 of the Dogger and carrying Sandrock, the total absence of the striatalus- 

 ox jurensis-hed?>, and a probable loss of a portion of the cominums-heds, 

 all of which are seen to be largely developed on the downthrow side 

 of the fault in the Peak, not quite half-a-mile distant. 



From the Peak to Blue Wyke Point that portion of the cliffs which 

 faces the sea presents a noble series of precipices, of which the ' alum 

 shale' at first constitutes the base, succeeded by iht jurensis-htds, 



