1857.] BOTANY OF PERTH. 265 



many narrow trap-dykes, some of which run continuously for 

 twenty to thirty miles. 



The town of Perth lies immediately on the Tay, in the bottom 

 of a basin or ample theatre, bounded by hills. In lowness of 

 situation and in the physical configuration of the surrounding 

 country, it resembles Dumfries ; and the climate of the two 

 places is also in great measure similar. The " statistical account 

 of Scotland " appears to me to give too favourable a view of its 

 meteorology or climatology. From the tables there given it 

 may be laid down that the number of dry to rainy days is more 

 than as 2 to 1 ; the mean annual amount of rain 25 '94! inches ; 

 the mean barometric pressure 29*8, and the mean annual range 

 of the barometer 2"1; the mean temperature 48*14, and the 

 mean annual range of the thermometer 57*5. Such results 

 would indicate climatological conditions very favourable to health. 

 The climate however appears to me to be more moist and varia- 

 ble than these statistics show. During a great part of the year, 

 spring, autumn, and especially winter, the banks of the river in 

 and around the town are seldom free from dense, cold mists, 

 which cannot fail to be inimical to health. The nature and 

 amount of the Lichenose vegetation of the neighbourhood, of it- 

 self indicates a moist condition of the atmosphere. There is a 

 marked difference in the temperature and hygrometric state of 

 the atmosphere between the town and moderate elevations above 

 it. The atmosphere on the hills above Kinfauns is often quite 

 clear while the town is enshrouded in mist ; and it is warmer in 

 winter and cooler in summer than that of the town ; hence the 

 sanitary condition of the villages, villas, and houses built on 

 KinnouU or Craigie hills, cannot fail to be, to a certain extent 

 at least, superior to that of town residences. 



II. Lichen-flora of the District. 



As my attention has been chiefly directed to the Lichenose 

 vegetation of the district, and as it is a subject of greater no- 

 velty, and hence greater interest, than the ordinary Phanero- 

 gamic vegetation, I shall notice it first in order. I can how- 

 ever here only notice the commoner Lichens, and even these 

 briefly, 



Usnea barbata, in its protean forms, is very common on trees 

 in the fir-woods on KinnouU Hill and neighbouring spurs of 



N. S. VOL. II. 2m' 



