The Kiso River is a 229 km-long river originated from Mt. Hachimori in Nagano Prefecture. Its main stream flows south-westward from the southern limb of Mt. Hachimori. It turns to the west after merging with Otaki River, a tributary originated from Mt. Ontake. It further merges with Hida River, another tributary from Mt. Norikura, and flows to the south through Nobi delta to Ise Bay (Pacific Ocean). In the ancient time, Kiso, Ibi and Nagara Rivers used to be entangled with each other around their mouths, which were separated by several flood control projects operated in the 18th to 19th century.
The Kiso River covers 5,275 km², and its valley is covered chiefly by accretionary complex sediments of the Mino belt. The Mino belt consists mainly of sedimentary rocks (sandstone and mudstone) with minor amount of chert as blocks or thin layers. The depositional age of the Mino belt determined by microfossils is Jurassic to earliest-Cretaceous, but some of chert blocks yield much older ages (Carboniferous to Triassic), that indicates they were included as exotic blocks at the formation of the acceretionary complex.
Other major lithologies are Nohi Ryolites and granitoids. The Nohi Ryolites is volcanoclastic rocks that are widely distributed in NW-SE direction covering middle-north Gifu and south Toyama Prefectures. The main constituent of the Nohi Ryolites is ryolitic welded tuff, a remelted (and recrystallised) volcanic ash by its own heat after deposition. Granitoids belong to Ryoke belt which is widely distributed in the middle to upstream of the Kiso River.

Kisogawa River rocks

Cobbles found in the Kisogawa riverbanks are classified into three. The largest group is Triassic to Jurassic accretionary prism sediments of the Mino Belt, which consists mainly of sandstone and mudstone associated with minor conglomerate and chert. The second group is various types of igneous rocks. Igneous rocks include volcanic rocks (e.g. andesite and ryolite) and plutonic rocks (e.g. granite and granodiorite). The former is an erupted magma that cooled and solidified rapidly on the surface. The latter is slowly crystallised in the deep crust that enabled large growth of rock-forming minerals. The ryolite found in this area is called the Nouhi Ryolite that is widely distributed in the Mino and Hida districts of Gifu Prefecture. The andesite is derived from the eruptions of the Ontake volcano. The plutonic rocks are from the Ryoke Belt, the Cretaceous to Paleogene granitic belt widely distributed in the Southwest Japan. Ryoke Belt also contains contact metamorphic rocks around the granitic bodies. Pelitic hornfels shown here is a metamorphosed mudstone by granitic intrusion. A heat of the intrusive body affected (burned) the surrounding sedimentary rocks and changed their mineral assemblages to those stable at the high temperature. As a result of contact metamorphism, the hornfels came to have finer and harder textures than the original medstone.
In addition to the above-mentioned rocks, manmade objects such as brick and concrete are also found in the Kisogawa riverbanks. You should be careful not to misrecognise them as natural rocks because some of these manmade objects look like natural rocks.

Sandstone
This sandstone mostly consists of quartz and feldspars (plagioclase and K-feldspar), being associated with minor amount of micas (muscovite and biotite). Contents of heavy minerals and lithic fragments are extremely low. Feldspar gives a dusty looking interior by alteration. This sandstone is crystalloferous and the matrix is relatively small. This type of sandstone is called " arenite " (this particular rock is called feldspatic arenite because it contains more feldspars than quartz).

Ryolite (Nohi Ryolite)
Ryolite is a felsic volcanic rock, an igneous rock crystallised at a shallow depth. Main constituent minerals are quartz and feldspar, accompanied by some accessory minerals such as biotite and tourmaline and secondary chlorite and epidote. Feldspar gives a dusty looking by alteration, whereas quartz looks clear as it is not affected by alteration. An embayment texture is found in the quartz of the lower left corner of the field of view (indicated with arrows). The quartz originally crystallised from the melt as beta-quartz that is stable at high temperature transformed into alpha-quartz with cooling. Phase transition from beta-quartz to alpha-quartz associates loss in volume that formed an embayment to the outline of the crystal.

Bulk sand

Quartz and calcic plagioclase occupy two-third of the total modal proportion. In addition to these minerals, K-feldspar and alkali feldspar (intermediate composition feldspar between K-feldspar and albite) occupy the most of the modal proportion of the bulk sand.

Heavy Minerals

Iron-titanium oxide (e.g. ilmenite) is the most abundant that occupies 43 modal%. A sum of pyroxenes and hornblende occupies same modal proportion as iron-titanium oxide. Zircon makes about 5 modal %. Other minor minerals are biotite, allanite and monazite, which are often found in granitic rocks. One alumino-silicate (Al2SiO5) mineral was found. This may be derived from a contact metamorphic rock that associates with Ryoke granitic intrusions.

Orthopyroxene composition (magnesium content: Mg#) has a sharp peak around Mg# 60-62, and also two other small peaks at Mg# 72-74 and 82-84 (although the latter two has only 1 or 2 counts). The peaks at Mg# 60-62 and 82-84 are considered to be the same as those found in the Nagaragawa-river. On the other hand, a peak around Mg# 58-60 found in the Nagaragawa river-sand is not found in Kisogawa river-sand. The peak around Mg# 60-62 coincides with the compositional range of the orthopyroxenes in the Ontake-1 tephra, the main tephra of the Ontake series. Although provenance of the other two compositional group are not identified, the compositional variation in Kisogawa orthopyroxene are interpreted as a mixture of at least three different origins.