The isotopic descriptions of present-day mantle derived rocks reveal the regional and global heterogeneities of the Earth's mantle with systematic variations. The mantle heterogeneities and systematic variations include Dupal anomaly, mantle array, mantle plane, and LoNd array. They led to the hypotheses involving the mixing of some mantle components. The mantle components are identified as follows ; DMM (most depleted component in the Earth), EM II (enriched component derived from sediments and subducted oceanic crust), EM I (end-member of LoNd array), HIMU (end-member of LoNd array with high U/Pb ratio), and PREMA (common and major components in the Earth's mantle, synonymous with, PUM, CHUR, UR and BSE). These mantle components could be generated by the principal processes of chemical separation, time effect and component mixing. The chemical separation process changes the parent/daughter ratios, the time effect process varies the isotope ratios, and the component mixing process between mantle components resulted in isotopic variations of the magmas derived from mantles. In the Earth's mantle evolution, two important global events occurred before about 3.8 Ga (1st event) and after 2 Ga (2nd event). The 1st event might be related to stratification of the early Earth, such as, the separation of the mantle and core, and/or the chemical stratification of mantle involving magma ocean. For a period of 3.8-2 Ga, the chemical structure of the mantle had been preserved. The second global event started at 2 Ga. This event might be related to the formation of the solid inner core from primitive liquid core, which might activate the mantle convection. The convection which mixed the mantle components should make the present isotopic variations of the mantle.
This paper is designed to examine the characteristics and formation processes of debris slopes on forested mountain sides. Two study areas were chosen. One is in the Mikouchi River Basin, Kanto District, Japan, and the other in the Muko River Basin, Kinki District, Japan. Both areas are composed of rhyolitic rocks overlayed by soil and tree growth. The slopes studied are characterized by their concave profile and steep inclination which is comparable to or exceeds the angle of a talus slope. From a point of view of debris movement, the slope is, as a rule, split into five slope segments, from higer position to lower position : free face, debris-transported slope on which debris can not cease its motion due to steepness and small roughness, high-positioned steep clitter, talus and low-positioned gentle clitter. Two different processes are suggested to the cause of the reverse grading phenomena of debris deposits. One is the sieving process through the grain flow. The other is the removal of the surficial fines of weathered material to the inner coarser at upslope followed by their deposition at downslope in that order through one-at-a time movement such as rockfalls. The fact that the study areas are covered by a mantle of tree growth and soil is thought to suggest that the built-up material on the slopes in question might have been deposited over a relatively short period of time, although a small amount of deposition still continued at present.