in the Neighbourhood of Edinburgh. 273 



These considerations prove to us, that if we would distinguish 

 between the marine and fresh-water formations of very early 

 epochs, we must form our judgment less upon any insulated re- 

 lics which may turn up, than upon an assemblage of organic re- 

 mains, considered in reference to a combination of geological cir- 

 cumstances. 



I shall, lastly, endeavour to sketch the true character of the 

 limestone of Burdiehouse, in reference to the beautiful specula- 

 tions of Mr de la Beche, upon the quietness of deposition in- 

 cidental to the formation of more ancient strata. 



Springs charged with the carbonate of lime, and issuing from 

 profound crevices incidental to one of the more early fissured 

 states of the earth's crust, had mingled their mineral contents 

 with the waters of some river, or of some fluviatile expanse, which 

 had sluggishly flowed through a marshy tract, principally over- 

 run by the creeping and gigantic stems of the mysterious Lyco- 

 podiacea?, and by a dense undergrowth of ferns, among which the 

 luxuriant growth of the Sphenopteris affinis was particularly 

 favoured. And hence the production of a calcareous deposit, 

 which, in [gradually and tranquilly congealing, had preserved to 

 plants possessed of such tender form and structure as the lesser 

 ferns, all the delicate divisions of their pinnae, or pinnulae, as well 

 as all the slender and linear character of their lobes, unaffected 

 by the violence of currents, or by any of the atmospheric com- 

 motions which a later and less heated condition of the globe has 

 invoked. 



So great, in fact, is this state of preservation, that we are 

 irresistibly carried back to a period, when, in conformity with 

 the distribution of a thermal ocean over various parts of the 

 globe, equatorial and polar states, by being rendered uniform, 

 would so adjust the temperature over the whole surface of our 

 planet, as to induce a quietness of deposition, which no forma- 

 tion perhaps more happily elucidates than the fresh-water 



LIMESTONE OF BuRDIEHOUSE. 



VOL. XIII. PART I. Mm 



