Re: After giving heat to milk till it boils a cream layer in formed ..How ?

I am not entirely sure I understand your question but here is what I think is happening: Normally, the lipids or fats in milk are held in suspension by weak forces between themselves and the proteins and carbohydrates also found in the milk. Heating the milk causes several things to happen:

1 - the proteins denature, breaking the weak bonds holding the milkfat in suspension, and
2 - the lipids/fats begin to melt and form larger globs.

The milkfat is less dense than the surrounding milk/water, so it floats/migrates to the surface of the milk. As the milkfat comes in contact with the colder air, it cools to form that thin layer you described.

I hope this explanation answers your question!

Kieran