They sound like Dog Lichens ( GW magazine Aug, pg 45 ). I had them and they
are difficult to rake out as the tines only break off little bits instead of
the whole patch. I wouldn't worry too much in a wild area but they did look
messy in the lawn. They look very much like grey/brown, flat bits of wood,
with curled up edges.

The article said - They cause no long-term damage. Remove by raking with a
spring-tine rake. Ensure soil is well drained and aerated.