By Zoe Kleinman
Reporter, BBC Dorset
Ammonites are one of the most commonly found fossils
Keen fossil hunters are expected to flock to beaches this weekend as unusually low tides are set to reveal more fossil-rich land usually underwater.
Dorset will see the year's highest and lowest tides on 10 and 11 September.
The monthly spring tides are at their most extreme this autumn, says the Maritime and Coastguard Agency.
This also means that when the tide comes back in, it will be higher than usual, the service warns.
"Before you go walking across sand flats and other beaches, check the tide times," said a spokesperson.
"They are often posted at the entrance to beaches. Don't take risks, tides can come in incredibly quickly."
It is a busy time of year for Charmouth Heritage Coast Centre in south west Dorset, at the heart of the Jurassic Coast, which runs for 95 miles from Exmouth in East Devon to Studland in Dorset.
Phil Davidson, a palaeontologist at the centre, described the conditions over the weekend as "about perfect" for finding fossils.
"I think there should be lots of finds, the sea has been rough over the last few days so there's every chance," he said.
"All the cliffs are made of soft mud, the tides wash away the soft mud and drags out the fossils ready-polished for you to find."
While the most commonly found fossils are ammonites (an extinct marine mammal) and belemnites (the bullet-shaped remains of ancient squids shells), larger bones are not that unusual, said Mr Davidson.
Palaeontologist Phil Davidson says conditions are perfect for fossil hunting.
"We've had people come in with rare bits of dinosaur who've just thought they were funny pebbles," he said.
"Most days we find odd isolated bones. It's not as rare as you would think but it is quite rare to find the whole skeleton."
Fossil hunters are not allowed to from dig fossils out of the cliff faces to prevent landslides.
In March 2010 the National Trust and Charmouth council took out an injunction banning an individual from fossil hunting on the Jurassic Coast for removing fossils from the cliffs.
"Wholesale digging into the cliffs, prospecting along fossil-rich layers, is dangerous and unacceptable," Helen Mann, National Trust property manager in Dorset, told the BBC at the time.