Is it possible to pursue M. Sc. in Geology after B.Tech.

You have completed your B.Tech in civil engineering. If you want you may do M.Sc Geology. But it is not a good idea. If you are interested in Geology you can do M.Tech in Applied Geology after your B.Tech. Your B.Tech course is treated equivalent to M.Sc Geology and you can join in M Tech.

M.Tech is also a 2 year Post Graduation course and there are many institutes offering this course.
You can study Mineralogy, Structural Geology, Geomorphology, Planetology, and Geological Engineering, etc.

NIT, Raipur, IIT, Roorkee, Sagar University and Kurushetra University are some of the institutes offering this course.

There is no connection between the two courses ie B.Tech in Civil - engineering and M.Sc in Geology. Hence if you are really serious in persuing this course, you will have to apply for B.Sc ( Pass - course) with your choice of Geology apart from two additional papers prescribed at degree stage such as Physics and Chemisrtry or Physics and Mathematics or even Physics and Chemistry. You will have to look out such colleges having the provision of this subject in the teaching cirriculam. Once you pass the B. Sc in Geology consisting of three year course, you will be eligible to apply for M.Sc in Geology course subject to securing of minimum qualifying marks fixed by the university for the intake of aspirants for such a course.
In you case, it would not be a wise decision because of wastage of valuable five years - three years for completing the degree and later two years for the post graduate course in Geology.
However, you can take up M.Tech course with some special subjects such as Geomorphology, Geological - engineering, Structural - geology etc.
For the persuasion of your course, you may make enquirers from Kurushetra University, Sagar University, Mumbai University etc.

No, you can not pursue Masters of Science (M.Sc.) in Geology after doing B. Tech. in Civil Engineering as you have not done B.Sc Geology degree and not studied geology at graduate level. Because most of the university / colleges require Graduation with the Geology as main subject from a recognized University / College.

But still if you want to study Geology at Masters level you can go for M.Tech. (Geology). Several University/ Institutes across country are offering this course. By doing so, your 4 years of B.Tech will also become saved.
List of University and Institutes offering M.Tech in Geology:
1. Indian Institute of Technology (IIT-ISM), Dhanbad
2. Indian Institute of Technology, Roorkee
3. Dr. Harisingh Gour University, Sagar University, Madhya Pradesh
4. Andhra University, Andhra Pradesh
5. Mumbai University, Mumbai
6. Kurushetra University, Kurukshetra
7. Sagar University, Madhya Pradesh
8. National Institute of Technology (NIT), Raipur, Chhattisgarh

Another option is that firstly you will have to do B.Sc. in Geology and then you will take admission in M.Sc. Geology.
Already you gave 4 years in B.Tech. then 3 years in B.Sc. and 2 years in M.Sc. Total time spent will be 9 years. that will be a very long period.
While if you will do M.Tech Geology, it will take 2-3 more years after B.Tech and Total time period will be 6-7 years.
So It is suggested that you should go for M.Tech instead of M.Sc. It will save 2-3 years in total.

Because you have B.Tech. degree in Civil engineering then you can opt Engineering Geology or Geotechnical engineering or Remote sensing or Geoinformatics etc.

Good Luck

It seems that Geology is your subject of liking but due to certain compelling reasons and circumstances you landed in B.Tech. Anyway, it is not late and you can cover it by going for doing B.Sc. with Geology first and then doing M.Sc. (Geology). B.Sc. Geology is a 3 years course and you will be incurring these 3 years before you go for your dream post graduation degree in Geology. There are so many good institutes for B.Sc. Geology and if you get admission in them then that will be a good beginning so that you can easily get admission in M.Sc. Geology.

Another alternative is go for M.Tech. in Applied Geology for which B.Sc. Geology is not mandatory and B.E./B.Tech. people are eligible for admission in it. This M.Tech. Applied Geology course is for 2 years and admissions are based on the score of entrance exams like GATE, TANCET and also 10+2 scores. After M.Tech. in Applied Geology there is scope for the positions of Geographers, Oceanographers, Geologists, Meteorologists, Seismologist, Completions Technologist, Processing Geophysicist, Researchers etc in various organisations like Central Ground Water Board, the Geological Survey of India, Coal India, Oil & Natural Gas Corporation, Mineral Exploration Authority, Hindustan Zinc Ltd etc.