‘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 pr 1a Becue, 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- 
podiacez, 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 pinne, or pinnulee, 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 
