206 Proceedings of the Royal Physical Society. 
In the Millstone Grit we find that a complete change in 
the flora has taken place. There is an entire absence—as 
far as my knowledge goes—of a single species of plant which 
occurs in the underlying Carboniferous Limestone or Cal- 
ciferous Sandstone Series. The Millstone Grit ushers in an 
entirely new group of plants—plants in many cases of a 
different facies from those which preceded them, but which, 
though rare in their occurrence, are identical in all respects 
with those of the overlying Lower Coal-Measures. 
The Millstone Grit, by which term I understand rocks so 
named by the Geological Survey, in Lanarkshire, Stirling- 
shire, etc., would appear to be less developed in Scotland 
than in England, where in Lancashire, according to Professor 
Hull, it attains a thickness of 5500 feet. 
In Scotland it contains many valuable beds of fireclay, 
which, in the neighbourhood of Garnkirk, Gartcosh, ete., are 
largely worked.! 
CARBONIFEROUS LIMESTONE SERIES. 
The Carboniferous Limestone Series is divisible into three 
groups, which are well seen in Stirlingshire and Linlithgow- 
shire. 
(a) A group of three or more limestones, with coals and 
thick beds of sandstone, ete. 
(b) A group of sandstones, shales, etc., with beds of coal 
and ironstone. 
(c) A group of sandstones, shales, etc., with several 
thick seams of limestone, and some coals and 
ironstones.” 
This threefold division is characteristic of the series in 
Scotland. 
Groups (a) and (c) are of a more marine type than 
group (b). . vs! 
Fossil plants are much less plentiful in this series than in 
1 Paleontologically the Lower Coal-Measures and the Millstone Grit form 
one series. 
*Mem. Geo]. Survey of, Scotland—Explanation of Sheet 31. Stirling 
(southern part), Lanarkshire (northern part), Linlithgow (western borders). 
Edin., 1879, p. 11. 
