Four experiments on strata formation in stream water using a straight flume were carried out with different detritus sediments: Experiment A (granules and fine sand), Experiment B (granules and very fine sand), Experiment C (fine sand and mud), and Experiment D (very fine sand and mud). In Experiments A and B, almost parallel interbeds of granules and sand were formed. In Experiment C, the mud was deposited in a lens-like formation. In Experiment D, bed boundaries were of a wavy shape, and flame structures were formed at the bed boundary of the sand and mud. Thus, it was concluded that Experiments A and B form parallel strata that are suitable to be demonstrated in a lesson on strata in the 6th grade of elementary school.

In this study, I analyzed university students’ answers to a comprehension test conducted after they studied a series of river landscape photographs related to river sedimentation from the perspective of diachronic thinking. The results showed that only a few students could recognize sediments above water level. This is because they could not understand the landscape’s past history, in which the river’s water level was higher, and thus they were evaluated as being inadequate at the interstage linkage stage of diachronic thinking. Thus, it is suggested that the students cannot recognize the causes and results of changes that do not occur simultaneously in the formation of landscapes. In relation to the development of logical thinking skills, university students need to be instructed in the sedimentation process with an awareness of the diachronic view of natural landscapes.