The purpose of this assignment is for students to synthesize field observations, petrography, and whole-rock chemical analyses in order to investigate chemical differentiation processes in a basaltic magma chamber. The students first complete a petrography lab on both hand samples and thin sections that represent a complete stratigraphic section through sill at Fort Lee, NJ. I then provide them with major- and trace-element data and a table of distribution coefficients for common phases that would be crystallizing from basaltic magma. I then ask them to discuss the chemical differentiation of the sill by writing up a 1-2 page interpretative summary based on their petrographic observations and the chemical data.