in showers. Autumn periods of four to six weeks of fine dry weather are common. Extended periods during autumn are calm. Extremely warm humid days in summer may result in destructive tornadoes. The growing season averages 178 days.
The geological history of Missouri ranges from pre-Cambrian to the present time. The oldest known rocks, which are exposed in the south-eastern part of the State in the region of the St. Francois mountains, are of igneous and metamorphic origin and include granites, porphyries and schists. Their exact age is unknown. A long period of erosion followed their formation before the first advance of the Paleozoic seas in late Cambrian time. These Paleozoic seas spread around and upon the old pre-Cambrian igneous masses during their advances over the State, and their deposits represent every period of the Paleozoic era except the Permian. All of Missouri except a small area in the extreme south eastern part and possibly a small area in the north-western part has probably been above the sea and subject to erosion since post-Pennsylvanian time, as no Mesozoic rocks have been found in the State and later marine deposits occur only in the south eastern part. The presence of Cretaceous deposits in neighbouring States indicates, however, that late Mesozoic seas may have ex tended into south-eastern and north-western Missouri. Large glaciers advanced from the north late in Cenozoic time and extended south of the Missouri river. These glaciers modified the topography considerably and left a mantle of drift over the north ern part of the State on their retreat.
The soils of Missouri present a wide variation. The soils of the northern part of the State were derived mainly from glacial and wind-blown materials, with the greater relative amount of rich loessal soils along the Missouri and Mississippi rivers. The west-central part of the State is underlain mainly by resid ual soils derived from the weathering of limestones and shales but contains alluvial soils. The east-central and Ozark regions of Missouri are in the main stony and gravelly and best suited to the raising of live stock, but finer and more productive soils occur along the Mississippi and Missouri river valleys and in the smaller stream valleys. These soils are derived from the weather ing of limestones, dolomites and igneous rocks of the Ozark region and from loessal and alluvial materials. The lowlands of
south-eastern Missouri are underlain by loany soils derived from water-deposited materials. The loams are of sand and clay, and when cleared of timber and well drained, are fertile: Government.—Three Constitutions, framed by conventions in 182o, 1865 and 1875, have been adopted by the people of the State, and a fourth (1845) was rejected. A Constitutional Con vention holding sessions during 1922-23 formulated and submitted to a special election on Feb. 26, 1924, 21 constitutional amend ments, but all the more important proposals were rejected.
In addition there was the body chosen in 1861 to decide the question of secession, which retained supreme though irregular control of the State during the Civil War, and some of whose acts had the force of promulgated constitutional amendments. The present Constitution (that of 1875) was a notable piece of work when framed. The term of the governor and other chief executive officers, which had been four years until the adoption of the Con stitution of 1865, under which it was two years, was restored to the long term. Various effective checks were placed upon legislative extravagance, and upon financial, special and local legislation gen erally. Among reform provisions, common enough to-day, but uncommon in 1875, were those forbidding the general assembly to make irrevocable grants of special privileges and immunities; and permitting the governor to veto specific items in general appro priation bills. The grand jury was reduced to 12 members, and nine concurring may indict. The township system may be adopted by county option, but has not been widely established, though purely administrative (not corporate) "townships" are an essen tial part of State Administration. St. Louis and Kansas City have adopted their own charters under constitutional provision. An amendment (1908) provides for initiative and referendum; emergency measures, and appropriations for the State Govern ment, for State institutions and for public schools are exempt, from referendum. The referendum may be ordered by the legisla ture or by a petition signed by at least 5% of the legal voters in each of two-thirds (at least) of the congressional districts.