More about NON -DEFINING CLAUSE

*A non -restrictive clause can refer to the whole of the main clause;
I had to queue for two hours in the train which[=and that ] wasn't much fun.
*Noun/ quantifier+ preposition+relative pronoun.
Consider the following pair of sentences .
Sandra has masses of grandchildren.Some of them are already married.
Sandra has masses of grandchildren, some of them are married.
At the party I  met Edward.Conversations with him were always entertaining.
At the party I met Edward,conversations with whom were always entertaining.
Harry had been eating spaghetti.The remains of it could be seen in his beard.
Harry had been eating spaghetti,the remains of which could be seen in his beard.
*Preposition+which+noun
In another rather formal construction, which can be used as a determiner.
She died aged 97 in 1999,by which time she had written 251 novels.
There may be problems with my visa,in which case my departure may be delayed.
NOMINAL RELATIVE CLAUSES[ I