358 BakeweWs Introduction to Geology, 



circumstances," he says, " attending the secondary strata is, 

 the convincing evidence they afford that, at different periods 

 of their formation, the earth had extensive tracts of dry land, 

 either islands or continents ; for, though the prevailing cha- 

 racter of the secondary strata is that of marine beds, yet we find 

 among them, beds containing exclusively freshwater shells, 

 and also terrestrial and marsh plants, and in almost all the 

 secondary strata, except chalk, though the organic remains 

 may be chiefly marine, we find remains of some freshwater 

 animal or terrestrial plant, which were probably brought by 

 rivers from the land, and floated into the ancient ocean. We 

 have, beside, the regular coal strata 3000 ft. or more in thick- 

 ness, abounding in terrestrial plants. We have also a great 

 thickness of freshwater strata in some parts of the oolite 

 formation; and again, the Wealden strata, more than 1000 ft. 

 in thickness, appear to have been deposited in a freshwater 

 estuary or river, which would have required a large continent 

 of dry land for its formation. Now, it is remarkable that, in 

 all the above beds, we do not find a single bone of any large 

 mammiferous land quadruped, nor even of the smallest species, 

 except in the anomalous instance at Stonesfield. To maintain 

 that such bones, not having been discovered, is no evidence 

 that they may not exist, appears to be making a retrograde step 

 in science. It is true that \\ the bottom of the sea has not 

 been dredged," to discover what species of animals have 

 existed in former ages : the geologist, however, can have no 

 need of such an operation, for the land beneath the former sea 

 has been laid bare, and is now exposed to observation over 

 an extent equal to the whole habitable part of the globe. 

 Every island and continent has formed part of an ancient bed 

 of the ocean, and that not once, but repeatedly. The absence 

 of remains of the higher orders of animals in all the secondary 

 strata, and the frequent recurrence of these remains in the 

 more recent or tertiary strata, appear to afford presumptive 

 evidence, amounting almost to certainty, that the higher 

 orders did not exist, at least in the northern hemisphere, till 

 an epoch subsequent to the deposition of all the secondary 

 formations." (p. 308.) The present volume has a copious index, 

 and a glossary of the principal fossils mentioned in different 

 parts of the work. Though on various occasions the author 

 evidently addresses his arguments to the consideration of ex- 

 perienced geologists, it is but justice to state that he never 



confounded. Mr. Bakewell, at p. 354. of his Geology, says, " I am fully 

 convinced that the Author of Nature has established laws for the pre- 

 servation of* distinct classes and orders of animals ; " but he adds, " these 

 laws are not limited by the artificial classifications of naturalists." 



