Type locality and use of name: The term Lower Block Coal was first used formally by Ashley (1909, p. 57-58), who earlier (1899, p. 90, 103) had cited lower block coal as an informal usage. In 1899 this coalbed was also designated as Coal III in the sequence in northern Clay County and in Vigo County, where Ashley had based his numbering of Indiana coalbeds. Numerous descriptions of this coal were taken from deep mines and outcrops around Brazil, which suggests that the type locality is about 2 to 3 miles (3.2 to 4,8 km) northeast of Brazil near the old mining town of Cardonia. Because the term Lower Block Coal has long commercial and geologic application, Indiana coal stratigraphers, following the classification of Hutchison (1967), continue to use the term with member status in the Brazil Formation.
Description: In northern Clay County the Lower Block Coal Member consists of dull to moderately dull banded coal that is slabby or blocky and that has two conspicuous sets of vertical joints, called slips by miners, which trend about N. 20/ W. and N. 70/ E, and are 0.3 to 2.0 feet (0.09 to 0.6 m) apart. The coal ranges from 0.7 to 5.8 feet (0.2 to 1.8 m) in thickness (Hutchison, 1960, p. 14). At many localities the Lower Block member has a bone coal at the base on which the main part of the coal rests directly. In places the upper part of the coalbed is separated from the bone coal by as much as 12 feet (3.7 m) of gray shale (Ashley, 1899, p. 522-596).
Gray shale that is hard, sandy, and thin bedded to massive and interbedded laminae of light-gray fine-grained sandstone generally form the roof of the coal. The floor consists of a gray sandy underclay or silty shale (Hutchison, 1960, p. 15-16).
Correlation: The Lower Block is the basal member of the Brazil Formation and has been mapped in southern Parke County (Powell, 1968), Clay County (Hutchison, 1956), southwestern Owen County (Kottlowski, 1959), and Greene County (Kottlowski, 1959, 1960; Hutchison and Hasenmueller, in preparation). According to Hutchison (1961, 1976, p. 24-25) the Lower Block is absent or unidentifiable north of southern Parke County, but Peppers (1982, p. 14-19) correlated a coal in northern Parke County with the Lower Block coal on the basis of palynology, which suggested a greater northward extent of the Lower Block coal.
A coalbed at about the same stratigraphic position as the Lower Block coal but lacking the blocky character and demonstrated lithostratigraphic continuity has been mapped in Daviess (Hutchison, 1971a), Dubois (Hutchison, 1964), and Spencer (Hutchison, 1959) Counties.
The Lower Block has been correlated variably with the Tarter Coal Member of western Illinois, the Willis Coal Member of southern Illinois, the Bell and Willis Coal Beds of western Kentucky (Wanless, 1939, p. 34, and 1962, p. 31; Kosanke and others, 1960, pl. 1; Hopkins and Simon, 1975, p. 182; and Searight, 1979, p. 84). According to Peppers and Popp (1979, p. 68), however, the Lower Block is correlated with the Tarter of Illinois, but not the Willis, and possibly with the 4A coal of western Kentucky. This latter Kentucky correlation has been denied by Williams, Williamson, and Beard (1982, p. 10).