AN EXTERNAL CORE-RETAINER 
by DR. A. A. MILLS 
Assistant Professor, Institute of Oceanography 
Dalhousie University 
Halifax, Nova Scotia 
INTRODUCTION 
For many purposes involving detailed 
study of the sediment-water interface (e.g. 
microbiological examination) it is desirable 
to obtain short cores in which the uppermost 
layers are completely undisturbed. 
The corers most commonly employed with 
this intentionl, 2,3 generally incorporate an 
internal core-retainer in which fingers of 
flexible metal or plastic are directed towards 
the axis of the coring tube. It has been 
found that such devices frequently agitate the 
top few centimetres of a loosely-packed or 
flocculent sediment, and also fail to retain 
sand or volcanic ash. 
APPARATUS 
This note describes a device which, by 
replacing the conventional retainer in the 
above corers, facilitates the collection of 
undisturbed samples from a variety of sedi- 
ments. Two models have been developed for use 
with deposits of varying consistency - one for 
stiffer sediments, the other for the more fluid 
silts or sands. 
The construction and mode of operation of 
this apparatus are shown in Figure 1. The 
corer is lowered in the open position A. Pene- 
tration in excess of a pre-determined length 
(6 in. has been found satisfactory) forces the 
collar upwards, allowing the supporting arm to 
spring free of the catch. Upon withdrawal from 
the sediment the sliding weight drives the 
retainer down the coring tube, over the bevelled 
edge of the cutting head, into the closed posi- 
tion B. When hauled inboard the corer is held 
vertically, the core-retainer carefully dis- 
placed, and a tightly-fitting cork disc pushed 
through the cutting head into the plastic liner 
The latter, with the enclosed core, is then 
easily removed and sealed. 
244 
REFERENCES 
1. Emery, K. O. and Dietz, R. S. (1941). 
Gravity coring instrument and mechanics 
of sediment coring. Bull. Geol. Soc. 
Amer. 52, 1685-171L. 
2. Hvorslev, M. J. and Stetson, H. C. (196). 
Free-fall coring tube: a new type of 
gravity bottom sampler. Bull. Geol. Soc. 
Amer. 57, 935-950. 
3. Phleger, F. B. (1951). Ecology of fora- 
minifera, northwest Gulf of Mexico. Geol. 
Soc. Amer. Mem. 6, 1-88. 
ACKNOWLEDGNENT 
This device was constructed and used 
aboard Lamont Geological Observatory's re- 
search vessel !'Vema!', and special thanks are 
due to Dr. C. L. Drake for helpful sugges- 
tions towards its design and practical appli- 
cation. 
