210 



EPOCHS OF VIOLENCE AND REPOSE. 



Let us now take a brief survey of the beds of secondary sand 

 and sandstone. The lowest or new red sandstone, appears to have 

 been formed, in an epoch of volcanic action, over a large portion of 

 the present European continent, which broke up the foundation of 

 primary and transition rocks, and scattered their fragments over the 

 bed of an ancient ocean. In many parts we observe a tendency to 

 form beds of porphyry, but the process appears to have been often, 

 more or less, interrupted by disturbing causes; and we observe por- 

 pbyritic beds, with well defined crystals of felspar, alternating with 

 sandstone of mechanical formation. We may further observe, that 

 in this epoch of disturbance there were long intervals of repose, dur- 

 ing which the beds of magnesian limestone and muschel-kalk, were 

 deposited in certain situations. 



The operation of mechanical causes is obvious in almost all sand- 

 stone rocks, and beds of conglomerate ; and the experiments of Sir 

 James Hall prove, that beds of loose sand, if permeated by steam 

 from saline water, at a high temperature, may be agglutinated into 

 sandstone. With respect to beds of clay, their formation, by sedi- 

 mentary deposition, will not be doubted ; but we are not certain that 

 in some instances, the matter may not have been ejected by sub- 

 marine mud volcanoes, containing the sul{)hur, iron, and saline mat- 

 ter, in which several of these beds abound. 



One of the most interesting circumstances attending the seconda- 

 ry strata is, the convincing evidence they afford, that, at different pe- 

 riods of their formation, the earth had extensive tracts of dry landy 

 either islands or continents ; for, though the prevailing character of 

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

 beds containing, exclusively, fresh-water 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 fresh-water animals, or terrestrial plants, which were 

 probably brought by rivers from the land, and floated into the an- 

 cient ocean. We have, beside the above evidence, the regular coal 

 strata, 3000 feet or more in thickness, abounding in terrestrial plants. 

 We have, also, a great thickness of fresh-water strata in some part 

 of the oolite formation, and again the Wealden strata, more than a 

 thousand feet in thickness, appear to have been deposited in a fresh- 

 water estuary or river, which would require 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 anoma- 

 lous instance of Stonesfield. 



To maintain that such bones not having been discovered, is no 

 evidence that they may not exist, appears to me to be making a re- 

 trograde step in science. It is true, that " the bottom of the sea 

 has not been dredged," to discover what species of animals have ex- 

 isted in former ages : the geologist, however, can have no need of 



