I’m sure my conchological friends won’t take offence when I say that every now and then I escape the world of normal pursuits and regular people to indulge my eccentric fascination for the humble shell.
Recently three of us ran shellsand workshops in Reading and Cambridge. The aim was to offer an introduction to the pleasures and merits of collecting and sorting shellsand. In all some 15 participants, ranging from novices and students to seasoned collectors, sorted a fraction of shellsand from Porthcurno. Porthcurno is a small village in the parish of St. Levan located in a valley on the south coast of Cornwall. It is approximately 9 miles to the west of the market town of Penzance and about 3 miles from Land’s End.
Porthcurno beach faces southeast, is narrow and has two embayments. Access into the second embayment is possible at low water. The sediments at this beach are intensely carbonate-rich, pale, biodiverse shellsands and gravels. Apart from numerous surf clam valves, shells of macro-mollusc species are seldom washed in.
To a conchologist shellsand is a magic substance which can give you hours and hours of shell-collecting pleasure (particularly in the winter months) long after you have returned from a trip to the beach to look for shells on the strandlines. To a geologist it is a sediment that contains 50% or more carbonate grains. The shellsands we are familiar with from the coasts of Britain and Ireland are skeletal (also known as biogenic) sediments because they are composed of biological remains: molluscs, serpulids, barnacles, bryozoans, echinoderms, forams, brachiopods, decapods, otoliths, ahermatypic corals.
Christine Street told us that finding shellsand is a matter of close inspection and luck. You find deposits of shelly material on different areas of beaches at different times, and tracking them down means getting to know your beach with its wind regime, tides and currents as well as its shape and topography. Her experience centres mainly around small Scottish islands and over the years she has visited a goodly number of them.
When prospecting for deposits it’s wise to have x10 lens around the neck which allows you to pick up a small sample in the hand and inspect it closely. What you see should give you a clue as to whether it is worth taking a sample home to sort under a microscope. By and large, shellsand is usually best found as the tide retreats. There may be a series of tidelines which may contain deposits. Where there are ridges and furrows on rippled sands, the shellsand collects in the dips, and also in the small scour moats that encircle scattered rock outcrops.
Generally speaking curved sandy bays are most productive. Some of the more interesting ones, at least on islands, are those coves with a southwesterly or northwesterly aspect where the prevailing current from the south or north sweeps past, into and around the curve of the bay and where there is a projecting curved rock outcrop at the mouth to prevent all the deposits being swept out again. Also those beaches which have a partially submerged reef can have interesting deposits that have been prevented from escaping on the outgoing tide.
These are of course broad generalisations. Beaches can be changed by very rough weather: most shells may be scoured away, although other interesting deposits, displaced from the seabed offshore, may be beached after a storm.
Bas Payne talked us all through collecting, cleaning, grading and sorting a shellsand sample. I outlined a few guidelines for identifying molluscs species and touched on the merits of recording species distributions for publication via a digital database which the Conchological Society manages. This biological information is accessible via the National Biodiversity Network (NBN Gateway) and is used to inform conservation management and biodiversity research. So our time is usefully spent. For most of the time we peered down microscopes, retrieving the shells we saw and naming them.
Many of the shells were no more than a millimetre or two. They are intricately and perfectly formed, amazing.
Some Shellsand Beaches with a Star rating
ORKNEY: Papa Westray, west of the southern jetty. HY4950. Small shells become trapped by rocks to the extreme southeast and float in on the incoming tide.
SHETLAND: Fetlar, the main beach in the south is Tresta. HU6190. Small shells are trapped mainly to the westward side by the projecting promontory, carried on the outgoing tide.
Eigg: The Singing Sands. NM4790. A north west beach with rocks at the southern end.
Tiree: Gott Bay. NM 0546. A very curved, wide southern beach. Small shells tend to be in the centre of the tideline and below, where the current swirls them. Central rocks may attract shellsand where the sea scours out the sand round them. Also Balephuil: Barnacle sand and shells. NL9541.
Coll: Feall. NM1454. The northern bay on the western promontory curves gently and attracts a long tideline of tiny shells on some days, mainly to the west.
Barra: Scurrival to the north. NF7208.
Eriskay: Princes Strand. NF7811.
Colonsay: Balnahard in the north-east. NR4490. Also Kiloran Bay: NR4098. A curved northwestern beach
Iona: Port Ban. NM2625. A small western cove of white barnacle sand. Many small shells may become buried.
St Martin‘s: St Martins Flats. SV9316. A vast sandy beach with many interesting shells.
Guernsey: Vazon Bay. On one occasions this beach yielded a small but very varied shellsand deposit close by the inland curving seawall.
Herm: Belvoir Bay and Shell Bay have magnificent tidelines of small shells/shellsand