Experimental shell regeneration in Mytilus edulis was carried out by means of covering artificial shell opening with glass slide. The ultrastructure and components of "organic membrane-shell" in the early stage of regeneration were mainly observed by means of scanning electron microscope, and studied in relation to mineralization. On the whole, the "organic membraneshell" consists of two distinct parts, "laminated thin membraneous layer" and "brown membraneous layer". The former is composed of several kinds of organic materials. The main component of them is "fibrous thin membrane", but some other kinds of fibers, spherules and particles are also found, prior to the formation of "brown membraneous layer". Of these materials, "fibrous thin membrane" is especially simillar to conchiolin which is organic matrix of calcified shell layer. Some of these materials seem to be related to the mineralization of regenerated shell, and also these seem to act as catalyzer for the nucleation of crystals on the inner surface of "brown membraneous layer". On the other hand, the latter is built up of organic granules, which aggregate and fuse with one another to make "brown membraneous layer". No crystal is observed in this layer. "Brown membraneous layer" is formed when there is a large space between mantle and glass slide, and acts as the protector for mantle. This layer resembles periostracum rather than conchiolin membrane, and seems not to be related to the mineralization of regenerated shell.

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The "Late Cretaceous" Nemuro Group is widely distributed in the southeastern part of Hokkaido and strikes ENE-WSW or NE-SW direction from the eastern end of Nemuro Peninsura to Kushiro City. The lithology of this group is characterized by the presence of "flysch-type" sediments, tuff breccia and dolerites, and is divided into the following eight formations in ascending order, viz. Nokkamappu, Otamura, Monshizu, Oborogawa, Hamanaka, Akkeshi, Tokotan and Kiritappu formations. The characteristic lithofacies for each formation will be described below. The Nokkamappu formation, the lowermost part of the group, consists mainly of tuff breccia, conglomerate, sandstone, shale, dolerite and andesite. The Otainura, Oborogawa and Tokotan formations are composed of shale intercalated with thin sandstone layers in some regions. The Monshizu formation is mostly represented by the coarse black sandstone. However, the upper part of this formation is composed of an alternation of sandstone and shale, and is frequently intercalated with acidic tuff. The Hamanaka formation consists of a flyschtype alternation of sandstone and shale, and is intruded by several sheets of dolerite in the east of Pomporoto. The Akkeshi formation can be subdivided into three parts, based on the difference of lithofacies or rock type. The lower part of the formation is mainly composed of light gray sandstone or an alternation of sandstone and shale which occasionaly shows intraformational disturbances formed by submarine slumping. The middle part chiefly consists of thickly bedded black sandstone, while the upper part is represented by an alternation of light gray sandstone and shale. In some areas, the intraformational disturbances can be observed in both the middle and the upper parts of the Akkeshi formation. Lastly, the Kiritappu formation mainly consists of conglomerate. In the west area, however, this formation additionally contains shale or sandstone member in its middle part. Most of the formations belonging to the Nemuro Group seem to continue without remarkable lateral change of facies throughout a long distance of about 100 km from the western part of the town of Akkeshi to Nemuro Peninsura. But in this concern, the only one exception is the case with the Hamanaka formation. The sandstones alternating with shale in the Hamanaka formation have a tendency to become finer, as it leaves westward from the Area III, and finally grade into shale in the Area II. The submarine slumping observed in some parts of the Akkeshi formation are variable in number from place to place. That is, in both the lower and the upper parts of the Akkeshi formation, submarine slumpings are well developed in the east area. On the other hand, slumpings presented in the middle part are predominant in the west area. Recently, the Nemuro Group has been considered to range from Late Cretaceous (Campanian-Maastrichtian) to Earliest Tertiary(Damian) in age. In the concerned area, the boundary between the Cretaceous and the Tertiary is estimated to be put within the sequence of the middle part of the Akkeshi formation by the present author.

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The Shigaraki-Yamato Plateau is situated in the central part of the Kinki Triangle (HUZITA, 1962) characterized by many active faults and alternate alignment of small-scale mountains and basins. This plateau is one of such mountain blocks uplifted by faulting. The basement rocks of this area is mainly composed of the granitic rocks of the Ryoke Complex. The thin sedimentary blankets distributed in this area can be divided into the following four groups from the geohistorical view-points : the First Setouchi Supergroup (early to middle Miocene), the Muro Group (middle to late Miocene), the Second Setouchi Supergroup (Plio-Pleistocene) and terrace deposits (late Pleistocene). The chronological variety of these sedimentary blankets advantages us to consider the change of the "movement rate " of the basement rock bodies since the early Miocene. In this paper, some problems concerning such sedimentary blankets are described based on the regional geological map (1:100,000) of this area prepared for the study of neotectonics mentioned above. They are summarized as follows: The Jigokudani, Tsugeno and Soni Groups, all of which belong to the Setouchi Volcanic Rocks, were clarified to be correlated one another with the detailed stratigraphic relationships among them. Consequently, the Muro Group is newly presented as a pyroclastic rock group including the previous three groups. The Ofuku Gravel Bed, which shows the typical mountain gravels facies and is distributed in the western part of the Shigaraki Plateau, were ascertained to be correlated to the Shigaraki and Kitamata Gravel Beds, both of which are called "the high level gravel bed" by KONDO (1968). Therefore, the stratigraphical situation of them is very likely considered to be the lower part of the Iga Formation of the Kobiwako Group. The low-relief eroded surface, which is one of the topographical features of "plateau", is considered to have been formed during some cycles of transgression and regression since the Miocene. The original form of the surface, however, might existed as a primary peneplain before the Miocene. The present low-relief eroded surface can be therefore regarded as a sort of stripped peneplain. The faults, most of which are reverse faults in outcrops, can be divided into four groups in their trends, namely E-W, NE-SW, N-S and NWW-SEE trends. The maximum vertical displacement after the sedimentation of the Second Setouchi Supergroup attains to 300-350 meters. Inferred from the fact that the remarkable structural difference between the First and Second Setouchi Supergroups cannot be recognized, the major stage of faulting is considered to be at least after the late Pliocene. This stage coincides almost with the general tectonic phase in the Kinki Triangle (HUZITA et al., 1973)

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Heulandite-clinoptilolite, mordenite and wairakite-analcime are widely found as alteration products of pyroclastic materials. In this article, the mineralogical properties of these zeolites are reviewed and the relationship between chemical composition in solid solution and the condition of formation of zeolite is discussed. In heulandite group, many investigators have reported no correlation between composition and depth of burial. In rocks of the same pyroclastic bed, however, high alkali heulandite has a tendency to occur in an earlier stage of alteration. High-calcium mordenite is found in rocks of relatively higher grade part of the zeolite facies. Hydrothermal experiments indicate that the Si/Al ratio of analcime varies as a function of temperature. But the silica content of natural analcime is not solely an indicator of temperature. In the solid solution of wairakite and its sodium analogue, high-alkali wairakite occurs in rocks of lower grade part of wairakite zone.

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