Green’s Dictionary of Slang

1. a piece, a portion, e.g. a lay of pannum, a piece of bread.

1821		D. Haggart Life 49: We had a weighty lay of them that same evening.
1866		W. Stamer Life of Adventure 1 25: The pay was, by his account, most liberal—one hundred and fortieth ‘lay’ he called it; in other words, I was to receive a one hundred and fortieth part of all the oil made on the cruise .
1873		Sl. Dict.
1879		W.J. Barry Up and Down 61: He offered me a ‘tenth lay,’ i.e. a tenth of the entire profits.

2. goods.

1821

D. Haggart Autobiog. 7: My want of knowledge of the flash kanes, where I might fence my snib’d lays.