THE OLD RED SANDSTONE. 39 
from the lowest to the highest form of life, should be, in 
some degree, a continuous chain; that the various classes of 
existence should shade into one anoiher, so that it often proves 
a matter of no little difficulty to point out the exact line of 
demarcation where one class or family ends, and another 
class or family begins. The naturalist passes from the vege- 
table io the animal tribes, scarcely aware, amid the perplex- 
ing forms of intermediate existence, at what point he quits 
the precincts of the one to enter on those of the other. - All 
the animal families have, in like manner, their connecting 
links; and it is chiefly out of these that writers such as La- 
marck and Maillet construct their system. They confound 
gradation with progress. Geoffrey Hudson was a very short 
man, and Goliath of Gath a very tall one, and the gradations 
of the human stature lie between. But gradation is not prog- 
ress; and though we find full-grown men of five feet, five 
feet six inches, six feet, and six feet and a half, the fact gives 
us no earnest whatever that the race is rising in stature, and 
that at some future period the average height of the human 
family will be somewhat between ten and eleven feet. And 
equally unsolid is the argument, that from a principle of gra- 
dation in races would deduce a principle of progress in races. 
The tall man of six feet need entertain quite as little hope of 
rising into eleven feet as the short man of five; nor has the 
fish that occasionally flies any better chance of passing into 
a bird than the fish that only swims. 
Geology abounds with creatures of the intermediate class: 
there are none of its links more numerous than its connect- 
ing links; and hence its interest, as a field of speculation, to 
the assertors of the transmutation of races. But there is a 
fatal incompleteness in the evidence, that. destroys its char- 
acter as such. It supplies in abundance those links of 
