THE 
GEOLOGICAL MAGAZINE. 
No. XVITI—DECEMBER 1865. 
ORIGINATI ARTICLES. 
——_+——__ 
I. On A SECTION DISCOVERING THE CretTACEOUS Bens aT ELy. 
By Harry Sererey, F.G.S., Woodwardian Museum, Cambridge. 
ert in containing small nodules of phosphate of lime, the 
Chalk shows no structural change where it terminates in the 
Ely section, but passes down almost imperceptibly into a dark 
greenish layer, and rests on it at an angle of about 35°. This 
greenish band, scarcely a foot thick, is full of nodules of phosphate 
of lime, and consists largely of glauconite. It is the Upper Green- 
sand, with Ammonites auritus, Terebratula biplicata, Dentalium 
ellipticum, and the usual local features. Nowhere can the passage 
of one rock into another be more marked than that of the Upper 
Greensand of this district into the Chalk. Conditions have changed 
a little with physical geography, but nothing suggests any break in 
time. About Cambridge the section is exactly the same; the Chalk 
just above is often flaggy, contains a few green grains, a little phos- 
phate of lime, and the commoner Greensand fossils mixed with those 
of the Chalk. Sometimes, however, there are some 10 or 12 feet 
of dark greyish-green marls above the Upper Greensand. They are 
separated by sharp lines of bedding from the Chalk, are very local, 
and perhaps only indicate a trifling denudation of the Gault. 
The fossiliferous bed, consisting of a soft dark-greyish marl, which 
is largely charged with dark-green glauconite and black nodules of 
phosphate of lime, is rarely more than a foot thick. Nowhere are 
there any hard beds in it, and nowhere any iron pyrites. In quarry- 
ing, the deposit is removed bodily, showing the old Gault bottom 
with hollows and unevennesses, often containing groups of associated 
bones belonging to one animal ; and sometimes discovering slight 
faults, which show the usual glistening sides. 
The Upper Greensand (d) has been found everywhere at the base 
of the Chalk, and extends obliquely over Cambridgeshire by way of 
Mildenhall, Isleham, Burwell, Swaffham, Quy, Waterbeach, Fen 
Ditton, Barnwell, and the zigzag of low Chalk hills extending round 
Madingly, Coton, Comberton, Barton, and Granchester, and so makes 
VOL. II. — NO. XVIII. MM 
