Explain that the cash book is a Journal as well as a ledger account?

Cash Book is both a Journal and a ledger:

Cash Book plays dual role_.as a boor of original entry (or primary entry) as well as a ledger. It is a subsidiary book because all cash transactions are, first recorded in the cash book and then from cash book posted to various accounts in the ledger. The recording of transactions in the cash book takes the shape of ledger account. As receipts of cash are entered on the debit side and cash payments on the credit side; there is no need of cash account in the ledger. Thus Cash Book serves the purpose of ledger account. It is clear from the above that Cash Book fulfills the function of a subsidiary book (Journal) and ledger both.