Vol. 52.] ON THE UPPER PORTION OF DUNDRT HILL. 683 



The Marlstone Rock crops out in the bank of Spring Farm rick- 

 yard, in the middle of East Duudry, and as it forms a small feature 

 it may be traced along the valley below the exposure of the Iron- 

 shot Oolite. A measure with the level yielded 70 feet, separating 

 these two well-defined rocks. Deducting from this 15 feet, which 

 other sections in the neighbourhood indicate to be the thickness of 

 the stone beds below the Ironshot Oolite, 55 feet are left us the 

 thickness of the Dumortieria-clays, and the presumed intervening 

 stone bed (that is, the ' bifrons-bed '). (See this section, Bed 7, and 

 Section I., Beds 27-30.) 



A point of very considerable importance is the above-mentioned 

 outcrop of the Marlstone Rock. It is evident that the officers of the 

 Geological Survey mistook this rock, which is an ironshot oolite, for 

 ' the Ironshot' (No. 2) — a bed so noticeable in the last section — 

 whereby they confused the bottom bed of this Section V. with the 

 top, which is 70 feet above it. Then, acting on this supposition, 

 and knowing there would be so much of the ' Inferior Oolite ' below 

 the * Ironshot,' they drew the base-line of the ' Inferior Oolite ' 

 somewhat below the outcrop of the Marlstone Rock, with this result 

 — that they have coloured in their map as 'Inferior Oolite' not only 

 areas occupied by what they call ' Midford Sands ' or ' Upper Lias ' 

 in other districts, not only Middle Lias, but even in all likelihood 

 a part of what they would term Lower Lias. And in this way they 

 have made the Inferior Oolite in places — for these remarks apply to 

 most of the hill — nearly 150 feet thick : that is, from where they draw 

 their line up to the top of the hill. The ' Inferior Oolite ' base-line 

 should have been drawn at the base of No. 5, about 15 feet below 

 the highest outcrop of the Ironshot Oolite ; whereas it is drawn in 

 the Geological Survey maps some distance below the outcrop of 

 Bed 10 — in fact, nearly 100 feet too low down. 



Going farther east, we notice on the northern escarpment of the 

 hill above Hill Farm certain exposures of the Marlstone and asso- 

 ciated beds giving the following results : — 



Section VI. — Above Hill Farm (A). 



ft. ins. ft. ins. 



Variabilis. 1. Pale drab stone. Bhynchonella aff. 



Moorei 4 



2. Purplish argillaceous ironshot stone. 



Beleranites ; Zeilleria aff. Lycetti ... 6 



3. Dense blue rock, derived. Hildoceras 



bifrons ; lumps of a pinkish stone, 



ochreous. Belemnites abound 3 



1 1 



SriNATi. 4. Marlstone Rock 2 



In this section a deposit laid down during the variabilis hemera, 

 containing derived fossils of the bifrontis hemera, rests directly upon 

 the Marlstone. In the next section, obtained from tumbled blocks 

 on the hillside, it does not. 



Q.J.G.S. No. 208. 3 a 



