Removed a small strip of land near the Lithuanian border, where the basic soils consist of Mesozoic layers from the Jurassic and archaic soils of the Permic, the rest of Latvia, which forms a strip of the great Russian lowland, is formed by dolomites of the Middle and upper Devonico, which follow one another from north to south with decreasing antiquity and are generally very little displaced. However, unlike what is noted in Estonia, ancient soils come to light, given that they were covered, between the end of the Tertiary and the beginning of the Quaternary, by a powerful blanket of glacial deposits, made up of fine mixed clays. with angular pebbles of various sizes, which have given the morphology of the town its current appearance. In places where the bottom moraine was able to settle regularly and where the melt waters could gather in basins, such as in the Riga-Jelgava depression (which is drained by the Lielupe River and clearly divides Latvia into two parts) and in the lowlands of Valmiera ( in NE Latvia) and Lubāna (between the hills of central Livonia and those of Letgallia), the terrain is now flat and formed as it is by glacial silt, it is generally well cultivated. Where instead there was a pause between a series of advances and retreats and even more where moraine lobes of glaciers met with their centers of origin placed in different directions, hills were formed there, having an appearance laughing at the frequency of lakes. Hydrography, after the glacial streams had opened passages in the most depressed areas, has had to adapt to this young morphology and the waterways are sometimes forced to make very long laps, as in the case of the Gauja, or to engrave the relief giving the places such a pleasant appearance as to induce the residents to use the denominations of Switzerland Livonian and Curonian. Forms connected with the glacial action, but never so frequent as to give the landscape, for vast stretches, a distinctive character, are the asar (where the too impetuous waters have brought the sands down, leaving a set of stones), the kames (rounded and regular shapes that originated from fluvio-glacial sands finely deposited in layers) and the drumlins ; peat bogs are also frequent, in places where there were poorly drained depressions. It should be added that along the coast, when the glaciers had retreated, there were two notable transgressions, probably in relation to the isostatic settlement, and the sea (about 8900-7900 years before the present era) covered some areas coastal, depositing fine sands, not very fertile, especially in western Courland.
To the west of the Riga-Jelgava depression three groups of hills can be distinguished, those of western Courland, west of the Venta, with Mount Krievu (190 m); the hills of eastern Courland, between Venta and Abava (Monte Kirmes, 200 m) and the hills of Talsi (175 m), between the Abava and the sea. To the east of the depression four main groups can be distinguished: the hills of Semigallia, along the left bank of the Daugava; the hills of Letgallia (289 m), which occupy the south-eastern corner of the country; the hills of central Livonia, which constitute the most important relief as they occupy an area of 3500 sq km. having an altitude higher than 200 m.; they are limited by the Daugava, Gauia and Aiviekste rivers and contain the highest elevation in Latvia (Mount Gaizinš, 314 m); finally, the hills of eastern Livonia, which continue in Estonia with Mt Munamägi (324 m), the highest elevation in the Baltic States, should be remembered. The coasts are generally low and sandy, bordered by dunes, with coastal lagoons and lakes, so much so that the main ports have had to find a place near the mouths of the rivers.
The northern end of Courland is formed by the sandy Cape Kolkas (Domesnäs), near the strait by which Latvia is separated from the Estonian islands, once infamous for the large number of shipwrecks found there. I drography. – By far the most important watercourse is the Daugava (western Dvina, in Russian Zapadnaja Dvina; in German Düna), which, for just under two thirds of its course (in all 1000 km.) In Russian territory, then acts as a border between the two southernmost provinces of Latvia, Semigallia and Letgallia, and divides the country into two parts. It enters Latvia 10 kilometers upstream of Piedruja, bathes Daugavpils (98 msm and 263 km. From the mouth) and after having received from the right the long tributary Aiviekste, emissary of Lake Lubāna, bends towards NNE., Runs along some rapids (slope 81 per thousand between the confluence of Aiviekste and Koknese), then flows into the sea in the southernmost part of the Gulf of Riga, after having bathed the latter city. It is 170 to 320 m wide. until the confluence of the Aiviekste, from 300 to 450 up to Riga and from 800 to 1400 in the last 12 km. Given the highly variable slope, the long period during which it is covered by ice (on average 107 days each year in Daugavpils and 37 in Riga), and also the highly variable regime (average flow rate of 661 cubic meters per second in Riga, with a maximum in April-May, at the time of the melting of the snow, and a minimum in January), it is not very suitable for navigation. Courland is for the most part tributary to the Venta (length 300 km; basin 11,200 sq km), which originates in Lithuania, flows from S. to N., forms a beautiful waterfall near Kuldīga (in contact between the dolomites and sandstone), it receives from the right the Abava (which runs through the picturesque region of Curonian Spit Switzerland) and has its mouth near Ventspils. At least partially independent course, after a meander broke the coastal dune and allowed a direct flow into the Gulf of Riga, there is also the Lielupe (or Aa of Courland), a very slow river that drains the waters of the Jelgava depression, 111 km long, formed by the union of the Mūsa with the Mēmele and swollen by copious tributaries, which form a fan-like network. NE Latvia. instead it is tributary of the Gauja (or Aa livone), which originates from the lake of Alauksts, bathes very picturesque regions (Switzerland Livone) and after 380 km. of very tortuous course flows into the Gulf of Riga, 30 km. to E. from the mouth of the Daugava, which it is probable was once a tributary through the depression of the White Lakes.
Latvia also has a thousand lakes, which cover 1.4% of the territory. The largest is that of Lubāna, which occupies a depressed area and is the residue of a larger lake surface, which originated in the diluvial period; it has an area of 81 sq. km., a basin of 2800, a maximum depth of only 2.5 m. and an average of 1.5, so that it was decided to drain it, also because it frequently overflows; its emissary is the Aiviekste. The Rēzna and Rušāni lakes in the hilly part of Letgallia also have the same origin, which is the region with the largest number of them. In northern Livonia the most important lake is that of Burtnieki, now only about forty square kilometers wide, but once much larger, while in Courland the best known and most studied lake is that of Usma (surface area 38.9 square kilometers, perimeter km.73.6, depth m. 15.1), fourth by surface but first by volume of water, located at the edge of the marine transgression zone; Mauritius, one of the five found in it, has been transformed into a natural park. The lakes, mostly elongated in shape, also have a diluvial origin, which occupy ancient glacial valleys (such as that of Ciecere in Courland), while the alluvial ones are usually not very large and with variable surface. There are also numerous coastal lakes, residues of ancient Baltic gulfs, transformed into lagoons and now in the process of disappearing (Lake Engure, Liepāja, etc.), while those around Riga (Juglas and Kīšu ezers) occupy more probably ancient river beds.
