Can anyone tell me how to read the contents of a TMemoField?

I'm using the assign method, but always i get a GPF error.

Below, my piece of code:

procedure TDicAtributo.LoadAtributos;
var
  Tabela : TTable;
  FDesc : TMemoField;
begin
  Tabela := TTable.create(nil);
  FDesc := TMemoField.create(nil);
  Tabela.DatabaseName := 'd:\optima\tec\crc\delphi';
  Tabela.TableName := 'tatrib.db';
  Tabela.active := true;
  Tabela.first;
  while not Tabela.eof do
  begin
        ...

        FDesc.assign(TmemoField(
           Tabela.FindField('Descricao_Atributo')));  {the GPF is here}
        ...
        Tabela.next;
  end;
  Tabela.active := false;
  Tabela.free;
  FDesc.free;
end;