Consolidation
The large number of small independent corps proved difficult to administer, and, by 1861, most had been formed into battalion-sized units, either by “consolidation”: increasing an existing corps to battalion size (usually in large urban areas), or by forming administrative battalions or brigades by the grouping of smaller corps (in rural areas). An official book of Drill and Rifle Instructions for the Corps of Rifle Volunteers and Volunteer Regulations were published in 1859 and 1861 respectively.
Read more about this topic: Volunteer Force (Great Britain)