CHICAGO, Dec 20 (Reuters) - Lumber futures at the Chicago Mercantile Exchange were lower early on Thursday, with a lack of activity in the cash market weighing on futures. At 9:56 a.m. CST (1556 GMT), lumber was $1.40 to $2.40 per thousand board feet lower, with January down $2.40 at $241.50 and March down $1.80 at $250.00. Traders reported long liquidation ahead of the holidays, and pressure from quiet dealings in the cash market. The traders said spruce was offered at $228 but there were no takers.