MIDDLE CHALK—SUFFOLK AND NORFOLK, 
473 
CHAPTER XXXIX, 
THE MIDDLE CHALK IN SUFFOLK AND NORFOLK. 
X 
General Description. 
The Middle Chalk of Suffolk has not yet been fully explored by 
anyone. Even the outcrop of its basement bed, the Melbourn 
Rock, has only been traced through a portion of the county, namely, 
from Mildenhall to Lakenheath, and this was done by Mr. Hill and 
myself in 1886.* Little is known of the higher beds, and no 
exposure of Chalk Rock or of beds referable to that horizon has yet 
been discovered north of the railway from Newmarket to Bury 
St. Edmunds. 
Rather more is known about this division in Norfolk, for the 
Melbourn Rock has been traced continuously through the county, 
and its course is indicated on the maps of the Geological Survey. 
Moreover, Dr. Barrois visited West Norfolk in 1875, and recognised 
the zones established by him at several localities mentioned in his 
“ Recherches ” (1876). Finally, Mr. Hill made some special explora¬ 
tion of the Middle Chalk in the north-western portion of the county 
(Sheet 69), and his observations have been published in the memoir 
on that sheet.! 
In Suffolk it is probable that the zones of Rhynchonella Cuvieri 
and of T erebratulina have a combined thickness of about 200 
feet, but they certainly become thinner northwards, and in the 
northern part of Norfolk their combined thickness is probably less 
than 100 feet. 
"5 ■ 1 
What relation the beds which contain Holaster planus in Norfolk 
bear to the zone of H. planus on the borders of Cambridge and 
Suffolk it is difficult to say. Seeing, however, that Holaster planus 
makes its appearance some distance below the Chalk Rock near 
Newmarket, it is possible that the, chalk which contains that 
fossil in Norfolk represents the highest part of the Terebratulina 
zone as well as the Chalk Rock beds. 
St r atigraphical Details . 
Zone of Rhynchonella Cuvieri. 
When the Bury and Soham Railway was being made in 1879, 
Melbourn Rock was recognised by Mr. Whitaker in the cutting 
south-west of Snail well, and it is traversed again by the railway to 
* See Quart. Journ. Geol. Soc., Vol. xliii. p. 563. 
+ Geology of the Borders of the Wash, Mem. Geol. Survey (1899). 
