THE CORALLIAN ROCKS OF ENGLAND. 329 



The HacJcness Outlier. — Having given a general description of what 

 may be deemed the average development of the Corallian beds in the 

 Seamer-Ayton-Brompton subdivision of the Scarborough district, 

 there remains one remarkable locality which belongs to this district, 

 though separated by denudation, and isolated on a lofty plateau. 

 This is the Hackness outlier, where, within a space of a few hundred 

 acres, may be seen a complete epitome of the whole Corallian system, 

 resting upon Oxford Clay, which itself may be traced down into the 

 Kelloway Rock. 



Omitting stratigraphical details, the following is a summary of the 

 beds which rest upon the Lower Calcareous Grit on Silpho Heights, 

 in descending order, with approximate thicknesses : — 



1. Upper Calcareous Grrit, partly in situ, and partly occurring ft. in. 

 as a fragmentary wash covering the fields to the north of 

 Loffeyhead Heights. 

 ( 2. Upper or true Coral Rag — a crystalline limestone made up of 



roundheads of Thamnastraa concinna 12 



The Bell-heads Limestone, or equivalent of the Coralline 

 oolite, made up of large oolitic granules in a dense greyish 

 paste, and containing towards the centre a strong band 

 of Thecosmilkc-ra,g full of fossils 18 



4. Thin bands of gritty limestones and sandy beds — Middle 

 Calcareous Grit. 

 [5. The Lower Oolitic Series. Small-grained oolites towards the 

 centre of the mass with flaggy limestones towards the top 

 and thick-bedded fossiliferous limestones towards the base 

 — the rock of the lime-quarries of Silpho and Suffield 18 



6. Lower Coral E»ag : a brown ferruginous coral limestone, with 

 brashy partings and interspaces, having a peculiar set of 



9 



** s 



a> o 

 t->. +j 



Ch a> 



p a 



£ 



^ | fossils 8 



g | 7. Basement- or passage-beds : a series of impure, gritty, and 

 o rather flaggy limestones, in some cases made up of commi- 



^ | nuted shelly matter, and generally very ferruginous ; quarried 



^ for walling and road-mending 24 



No. 1. The Upper Calcareous Grit is limited to a small space, 

 chiefly between Loffeyhead Heights and Silpho. It presents the 

 usual characters so well recognized at Pickering and elsewhere to 

 the westwards ; but this is the only locality where we know of its 

 preservation in the eastern area. From its existence here as a frag- 

 mentary outlier, we may perhaps infer that it covered the Ayton Rag 

 in the same way as it does that of the region to the west of Pickering. 

 Owing to partial denudation and weathering on an exposed plateau 

 600 ft. above the level of the sea, the more indestructible Coral Rag 

 is thrust through it in knobs and hillocks, and might seem at first 

 * sight to overlie it ; but a careful examination of the ground on 

 Loffeyhead Heights, where a complete sequence may be traced, failed 

 to indicate its infraposition. The Coral Rag may there be seen dis- 

 tinctly reposing on the Bell-heads oolite, though the latter is at a 

 much greater elevation than one would expect without calling in the 

 aid of a fault, or sharp roll of the beds ; and on the Bell- head itself 

 the fields exhibit the Upper Calcareous Grit in such a position as 

 renders it impossible for it to be underlying the Rag. A mass of this 

 Upper Calcareous Grit, apparently bedded, was found to contain the 



