two layers of rock contain trilobites that have the same body morphology, however one rock layer is a shale and the other is an ironstone. Can these two layers be used for correlation?a-no, layers with the same lithology can only be used for correlation purposesb-No, the ironstone has been altered by oxidation and thus is older that the shalec-Yes if the trilobites are the same then the layers were formed at the same timed-Yes the ironstone is the altered remains of the shale and thus the layers are the same