Yes, you can appear in the IIT JAM Exam. As per the Eligibility criteria for Geology subject in IIT JAM 2018, your graduation must fulfill the following statement:

“The graduation degree must have Geology for three years/six semesters and any two subjects among Mathematics, Physics, Chemistry and Biological Science”

And as per my knowledge, your degree do fulfill the above statement.

Hope it will be helpful..!!

All the best..!!