ORGANIC REMAINS. 
101 
remains are din’erenl in the din'erent strata. In the transition 
rocks arc found vaidous kinds of coral, niailrcpore, crinoiihe, tri- 
lohites, and other similar organic snbstanccs, very many of whicli 
are altogether ditferent from such as are known to exist in the 
ocean at the present day. In many cases, not only has the spe¬ 
cies or genus, hul the ty|)e or general structure and form disap- 
pearetl, so that amongst the living races there is none that hears 
more than a distant l escmhlance to such as fdletl in countless mul- 
titiules the waters of that ancient earth. The old i-ed sandstone 
and metalliferous limestone which rest upon the transition rocks, 
also contain these lemains, and in greater ahuiulance, but they 
arc of a ilillerent kiml, bearing however, a greater rescnddancc 
to such as are found in the transition strata than to the tribes now 
inhabiting the sea. The coal measures abound in fossil remains 
and impressions of plants, but shells arc rare, and in many cases 
altogether wanting. The iMagnesian limestone which comes 
next has many shells, petrified tishes, and the remains of an am¬ 
phibious animal of the genus Monitor are found in it. In the 
new red saiulstone organic remains arc so very rare, that the ex¬ 
istence of any, of whatever kind, in it was atone time denied by 
geologists. In tlic Lias first make their a])pearance the Ichthyo¬ 
sauri and Plesiosauri, large reptiles bearing some resemblance to 
the alligator, but furnished with paddles instead of legs and feet, 
as instruments of motion. Kxtending upward througii the strata 
to the chalk, they have with the turtles, crocodiles, and other 
lizards that are associated with them, jirocurcd for this, the name 
of the saurian period in the history of the earth, or the age of 
reptiles. The Oolite abounds in organic remains consisting of 
corals and other shells, the reptiles of the Lias, and several dil- 
ferent kinds of Pterodactvle; a creature in which were united the 
characters ofa reptile, a bird, and a mammal, with wings like a 
hat, and supposed like him to have liecn abroad in search ol lood 
in the dusk of the evening or at night. Here also lor the lirst 
time do we lind the remains of a (piailruped inhabiting the land. 
Tliey arc the hones ofa species of Opossum. 
In the strata still above, other remains of other genera occur, 
but traces of land animals arc either few in number or altogether 
wanting. Chalk which was long regarded as a precipitate from 
\vater highly charged \\'ith carbonate of lime, jiroves inuler the 
microscope, to bean aggregation of shells too minute to be distin- 
guisbable by the naketl eye. It is not till we come to the most 
recent strata and a beil of clay, sand, and gravel, co\'ering 
all the other formations, that wc fmd evidence that the earth 
has at a former, distant era, been thickly peopled by (|uadrnpcds 
resembling those which now occupy its surlace, though ilillering 
from them in some I'espects. It is in this ujipcr bed that the los- 
sil bones of Elephants, Hippopotami, and Kbinoceri occur. 
From these facts it may be inferred, that these dillerent strata 
were formed in succession, and that each in its turn has been up- 
