- Limestone is a kind of sedimentary rock
- Nearly all fossils are found in sedimentary rock
- Therefore, fossils can be found in limestones

- Fossils can be found in limestones
- A fossil seashell is a kind of fossil
- So, a fossil seashell can be found in a limestone

Therefore, a fossil seashell can be found in a limestone
Which rock is most likely to contain fossil seashells?
- A fossil seashell is a kind of fossil 
- Limestone is a kind of sedimentary rock 
- Nearly all fossils are found in sedimentary rock