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HOLGATE : CARBONIFEROUS STRATA OF LEEDS. 
generally decayed or have gone to form a nodule of very clayey iron- 
stone. After repeated examination the idea forces itself upon one 
that it does not represent a forest growth with mud poured amongst 
it, but that it represents a quiet nook, with water plants growing and 
with stray leaves and bits of floating wood becoming water-Jogged 
and quietly sinking to the bottom, and that the whole was so gently 
done that the mud entombed the growing plants without disturbing 
them, and those which had sunk so as not to alter their form. 
Ironstone nodules are numerous and lie in layers, sometimes 
they unite and make a continuous plate. The nucleus of these 
nodules is always animal or plant remains. The plants do not appear 
to have had the power of concentration which the animals have had, 
and are softer and do not contain so much iron, generally the remains 
have been damaged before the concretion has been formed, some- 
times it is the frond of a fern, and if so it will be perfect ; some have 
acted curiously, they have for/ned about the stigmarise or lepidostrobus 
and have completely entombed it without injury, a sufficient quantity 
of carbonate of iron having filtered through the nucleus has sufficed 
to preserve every cell. Upon breaking the nodules into pieces we may 
take out the specimens and examine them under the microscope. 
Brown and Grey Binds mark a period of transition from the 
state of things above named to one in which the course of the 
stream was altering, or that it was quickening in speed and bringing 
down more sand. Specimens are not well preserved in it ; sometimes 
we find that the stream was actually running over it, and that as it 
receded it left its ripple marks and worm burrows which hardened, 
and when the next flood came, bringing with it sand even coarser 
than the last/ it deposited it on the uneven surface and a cast was 
made of it which has remained to the present day. 
Colour of strata is a good guide to the kind of fossils we shall 
find, as well as to the physical changes to which the strata have been 
subjected since they were deposited. Black hard shales contain the 
remains of fishes or molluscs and plants. Blue bind contains plant 
remains which are not numerous but well preserved. The stones 
contain only casts of plants, the passage of water through them 
as long since removed any vegetable remains there might be. 
