I don't understand earldoms.

I am researching Cornelius McLean Sr who died on SEP 12, 1836, in Washington DC USA, at the age of 62. I am trying to determine if he is connected to the family of John McLean (b. ABT 1748, Berkley Manor Scotland) who married Mary Jean Steele (b. ABT 1738) d/o Rev. John Steele and Margaret Hutchinson of Cumberland County PA USA. Supposedly, John was the son of the Earl of Berkley McLean and Lady McLean of Scotland.

Is anyone familiar with an earldom of Berkley in Scotland?

There are streets named Berkley in Glasgow. Could that have anything to do with a previous earldom?

Is anyone working on this McLean line? I want to know if any of John's siblings immigrated with him.

Thank you.