How did the iron filing patterns show attractive forces between magnetic poles?

When the magnet is placed on the glass, it is attracted to the iron filings. The pattern of the iron filings shows that the lines of force that make up the magnetic field of the magnet. Also, The lines of force of north and south poles attract each other whereas those of two north poles fend off each other.

answer: the metamorphic rocks are formed when they are exposed to high pressure and high temperatures. this happens when one of the earth's plates comes in contact with the other plate by traveling in opposite directions, straight into each other or slipping under one another. the friction that is caused by this activity results in   melting of rocks and when it cools they are known as metamorphic rocks. this process needs a controlled amount of pressure and temperature otherwise it may turn into magma.