CHAP. XXXVIL] IN COAL STRATA. 305 



absence of air-breathing quadrupeds or birds, served 

 to constitute negative evidence, of peculiar signifi 

 cance, in reference to the coal-measures, because, as 

 before stated*, they contained the monuments of 

 shallow freshwater swamps, and often of surfaces of 

 land covered with a luxuriant vegetation of terres 

 trial plants, some of the buried trees of which still 

 remain with their roots in their natural position. 

 That we should never have found, in such deposits, 

 the remains of air-breathing creatures, except a few 

 insects, that we should not yet have met with a 

 single mammifer or bird, or lizard, snake, or tortoise, 

 or the faintest indication of their existence, seemed 

 most inexplicable, and led many geologists to em 

 brace the opinion, that no beings having a higher 

 organization than fishes, were created till after the 

 carboniferous strata had been elaborated. 



During my stay in Westmoreland county, I was 

 indebted to Dr. King for the most active assistance 

 in the prosecution of my inquiries. He kindly de 

 voted several days to this object, and we first visited 

 together a stone quarry in Union township, six miles 

 south-east of Greensburg, on a farm belonging to 

 Mr. Gallagher, where the foot-marks had been first 

 observed, standing out in relief from the lower sur 

 face of slabs of sandstone, resting on thin layers of 

 fine clay. These slabs were extracted for paving- 

 stones, and the excavation was begun in the bank of 

 a small stream, where there was at first a slight 

 thickness only of shale overlying the harder beds ; 



* See ante, p. 245, 246. 



