I. Metamorphic rocks
There are mainly Proterozoic metamorphic rocks and pre-Devonian metamorphic rocks. The main minerals of Proterozoic metamorphic rocks are syenite, potash feldspar and biotite. Rough structure and clear schist. The upper part is thick gray phyllite, leaflike cyan slate and thick reddish brown schist or grayish brown schist, and the lower part is brown gneiss. This kind of lithology has a small exposed area and is mainly distributed in the northeast peak area of Shatian. Pre-Devonian metamorphic rocks are composed of sandstone, shale and a small amount of phyllite, slate and hard sandstone. The strata are divided into upper, middle and lower parts, and the rocks in each part are slightly different. The upper tip of the lower part is cyan, brown and light red thick flaky sandstone, the upper part is gray and gray-green slate and shale, and the upper part is hard sandstone rich in manganese and iron. The riverbed in the south of Xinfeng City is in the middle of pre-Devonian, and the upper part is at the foot of the gentleman's palm in the north of the city, at the southern foot of Qingshanzhai, and near the hills of Liang Shuang. Pre-Devonian metamorphic rocks are mainly distributed in Yingpan, Cao Xi and Maweitian in Huang Qi, Yuecheng, Liang Shuang and Ban Ling in Fengcheng, Zhangtiankeng, Keluo, Meizikeng, Yanggutian and Luobei in Matou.
Second, intrusive rocks
The biotite granite in the third stage of early Yanshanian (early Jurassic) is gray and light gray, and it is light flesh red after weathering. The composition minerals are potash feldspar and quartz, with a small amount of mica, granite structure and all-crystalline massive structure. Mainly distributed in the western and southern areas of Shatian, Meikeng, Qingshui and Huaxi.
Third, spew out rocks
From the end of Mesozoic to Tertiary, rhyolite, microcrystalline granite, dark brown, yellowish brown and gray, with fine structure and layered structure, covered with granite. It is mainly distributed in the northwest of Meikeng and around Junzizhang and Yunjishan Nature Reserve in the north of Fengcheng Street.
Fourth, limestone.
It belongs to the Early Jurassic of Mesozoic, and its outcrop is in the shape of an isolated hill, which is distributed in Laishi, tangcun and Jiyun Mountain in Huilong, with an area of about 1 km2. The color is grayish white and dark green, with many white calcite veins. In addition, limestone is distributed in Shatian, Fengcheng, Huang Qi, wharf and other places, inclining to the west and buried deep under the rock stratum.
Verb (abbreviation for verb) sedimentary rock
It is mainly composed of modern river alluvium, which was formed by Holocene and Pleistocene river alluvium. The lithology is loose gravel, sandy clay, loam, silt and peat. It is mainly distributed in Xinfengjiang River Basin, Meikeng, Liang Shuang, Qiangkeng, Layered Pit, Daxi, Huilong, Shatian, Tian Yao River and its tributaries, which are exposed in strips and form river alluvial terraces. The territory is dominated by flowing water landforms, and only Laishi, Tangcun and Xincun in huilong town are karst landforms. Yanshan movement occurred at the end of Mesozoic and Cretaceous, and the land rose sharply, accompanied by granite intrusion. Under the action of flowing water, after long-term weathering and erosion, the granite originally formed underground gradually emerged from the mountain, while most of the strata originally covered on the granite were eroded away, forming a low-grade granite hilly area in the west, with round mountain and loose terrain. Due to less weathering erosion of granite in the east, Devonian, Carboniferous, Permian, Triassic and Jurassic strata are preserved more, forming divided and broken hills and platforms. In Tertiary, influenced by Himalayan movement, the south continued to uplift to high mountains or low mountains. Due to the influence of faulting at the end of Mesozoic and the beginning of Tertiary in central and northern China, all the intermediate-acid extrusive rocks are rhyolite, covered with granite, forming the highest mountain group in central and northern China. In the Quaternary, neotectonic movement occurred, which caused the land to rise and fall. The rising areas are high hills and low hills, and the falling areas are alluvial plains.
According to the geomorphological causes and morphological characteristics, the land potential in the county is inclined from the middle to the east, with low mountainous areas in the east, hilly areas in the southwest and Zhongshan areas in the north-central part. Geomorphology is divided into eastern low mountainous area, western hilly area, central Zhongshan area and hilly basin area along the river (river).
First, the eastern low mountainous areas.
East to the county boundary, the west boundary starts from the vast area east of Matou Banling, Qiangkeng and Shijiao Line. The mountain is relatively gentle, the peak is generally more than 400 meters, and the slope is 30 ~ 50. A few slopes in the east, especially the peaks of Daxi, have formed multi-level shoulder terrain in the eastern mountainous area of this area due to differential erosion. The peaks on both sides of the road from the county to Matou are the most obvious, and most of the peaks in the east are above 800 meters above sea level. The peaks on the east, west and north sides of the valley are relatively short, generally around 300 ~ 400 meters. There are many small valleys between the peaks, the riverbed is in the primary stage, and there are many waterfalls in the river, but the mountains are not high and the flow is not large.
Second, the western hilly areas.
To the west of the county boundary, it starts from Huilongniu gutang and Puchang in the north, Zaohekeng in Sha Tin, Zhu Chi 'ao, Shi Yang, Yanshui, Tie Liang, Xialaikeng in Tian Yao, Angtian Lion and Tian Fei Cliff in the north, which is generally below 500 meters above sea level, but there are also peaks over 500 meters at the junction of Conghua and Fogang in the south. In the north, except for two limestone peaks and a few sand shale peaks in Huilonglai Stone and tangcun, most of the other peaks are made of granite. Because granite contains potash feldspar and quartz, in which potash feldspar is easily weathered, quartz sand particles that are not easily weathered are loosely piled up, there is no steep peak in the west, the ridge line is not undulating, the mountain is round and gentle, the slope is mostly below 30, the terrain is broken, there are irregular basins and valleys between mountains, and rivers are not well developed.
3. Zhongshan District in central China.
Between the east and the west, the rock composition is rhyolite and the lower part is granite. Because rhyolite is ejected late, the lithology is difficult to be weathered, and it is in the early stage of weathering and erosion cycle, so the terrain is high and steep, forming a huge dome structure. Mountains and rivers are everywhere, becoming the natural watershed between Dongjiang River and Beijiang River. In the east and south, the rock is granite, the mountain is more than 800 meters high, and the ridge line is round with little fluctuation; Most of the rocks in the north are rhyolite, with protruding peaks and steep cliffs and uneven ridge lines; There is a canyon in the middle. As the canyon extends around, many long, narrow and flat valleys are formed, both in the southeast and northwest directions. The height of the valley bottom generally increases from south to north, generally between 400-600 meters. In the middle of the valley, a mountain stream (river) rushes out from the mouth of the valley, forming bottom alluvial, in which the river swirls, which is one of the rice planting areas.
Four, along the river (river) basin hilly areas
Xinfengjiang River and its tributaries meander with Beijiang River system, flowing into Xinfengjiang Reservoir from the middle east and Beijiang River from the northwest. There are many river alluvial deposits on both sides of the river, forming a series of mountain valley basins, and forming a long hilly zone with relative elevation 100 meters at the edge of the basin. From this line to the north and south, below 500 meters is a first-class low mountain, and on both sides of the river are second-class terraces. The first-class terrace is about 15 meters high, and the terrace is flat, which has been reclaimed as farmland. The second terrace is about 30 meters high, and cash crops such as fruits and tea are also planted.