Complex sentence: Some pieces of continental crust may be subducted down to 150 km or more and then returned to the surface, where they can be recognized by unusually high-pressure metamorphic assemblages including coesite and even diamond.
Split into simpler sentences: Some pieces of continental crust may be subducted down to 150 km or more and then returned to the surface. These can be recognized by unusually high-pressure metamorphic assemblages including coesite and even diamond.