Moving 17th Century Soldiers

Demi-Hearse Formation

several in sequence, the first being "Pikes stand, musketeers advance before your front of pikes and close your divisions." - see animation

This configuration is especially suitable for two units of musketeers exchanging fire if there is no distracting cavalry attack. Colonel Barriffe recommends this  for its stability and solidity while being able to deliver as much shot as other formations but: "...with half the danger."* 

That "half the danger" is of keen interest to the pikemen.  The musketeers shelter them from enemy fire.  They remain protected until the battle shifts to the point their services are required (in which situation the formation of musketeers may be reduced as illustrated in the animation). One can conjecture the Demi-Hearse was historically a favorite of pikemen.

The animation illustrates two methods of deploying the musketeers.  The commander may utilize other means, however, even a maneuver as simple as the files of musketeers firing and countermarching.

*Chapt. 76, Military Discipline...

Sergeant Subtlelus says:
Protected from enemy shot, the pike division remains full and ready to deliver when the course of battle may be precariously balanced on a moment.  The pike can come to the shock with the numbers to try the fortune of the day.