138 
COAL ON SECONDARY STRATA. 
able collieries. This is the case in the North 
of Yorkshire, and at Brora in Sutherland. 
There are lignites, arising from peat forests 
of the present epoch, in the North of Ger¬ 
many, where the carbonized substance is 
extracted in blocks cut with the hatchet, 
and the supply is abundant. In the Rhine 
valley near Bonn, occurs a tertiary deposit 
called the brown coal formation from its 
containing bituminized wood in various states 
of mineralization; some trees apparently 
in situ, rooted where they grew, others 
prostrate and decayed. The wood is par¬ 
tially used as timber in building. The cir¬ 
cumstances shew the growth and entomb¬ 
ment of a forest on the banks of a fresh¬ 
water lake, whilst the surrounding district 
was agitated by the volcanoes whose ancient 
eruptions have contributed to the pic¬ 
turesque features of the enchanted river.” 
In the country of the Albigenses, coal is 
extensively worked in a freshwater tertiary 
formation. The firm blue limestones and 
regularly bedded shales, interstratified with 
carbonaceous matter, are on the i)lan if not 
on the scale of the true coal fields; but many 
