10a Wisdom of a Frenchman. [6 letters] ?O?M?N
15d Legal periods with John, [8 letters] S???N????
13d Yours truly in mud cave deciphering handbook. {4 & 5 letters] ?A?? ?E???
18d Towel lying over boot., [5 letters] IS THIS WELLY IF SO WHY?
19a Gradually diminish river and county. [4 & 4 letters] ???? DOWN