140 Mr. Warcuerr’s Odfervations on Bitummous Subfiances. 
fection, exhibit the concentric circles of their annual growth, with 
this difference, that the trunks have been fo compreffed as to be 
nearly flat, fo that the circles appear like parallel lines connected 
at their extremities by a {hort curve. 
I did not obferve fuch an appearance at Bovey; but this would 
depend upon the pofition of the trunks of the trees, in refpec&t to 
the fection of the ftrata. 
Chaptal *, Troil +, Bergman}, and many others, have been of 
opinion that the rapt: henge: is wood which has been charred by 
the heat of the lava. But I cannot difcern why it fhould be fup- 
pofed that it has been aéted upon by fire, any more than that the 
Bovey coal has been fubjected to the effects of the fame agent. 
‘The qualities of the two fubftances are the fame; and as (from Arch- 
bifhop Troil’s and Profeffor Bergman’s account) the furturbrand is 
‘ftratified, I. think we may venture to pronounce that the circum- 
{tances 
* Elements of Chemifiry, vol. iil. p. 199. 
} Von Troil’s Letters, p. 43. 
t Quid de ligno fofhli Iflandiz fentiendum fit, gnaro in loco natali contemplatori 
decidendum relinquimus. Interea, ut cum Vulcani operationibus nexum credamus, plures 
fuadent rationes, quamvis huc ufque modum ignoremus, quo fitum texturamque ad- 
quifiverunt hee ftrata.. Scilicet truncis arborum perquam crafts conftant, qualis in 
TMlandiA nullibi reperiuntur, et ne quidem hoc tempore crefcere poffe videntur. Hi fitu 
horizontali in ftratis multorum pedum craffitiei congefti funt et petroleo plus minus 
penetrati, non jam molli, fed optimé indurato, a quo tam nigrorem, quam flammz fub 
deflagratione qualitatem mutuantur. Sed quod in Ps ae attentionem meretur, eft 
truncorum in lamellas planas compreflio. 
Ponamus truncum arboris cujufdam tranfverfim fe€tum, hinc, uti notum eft, figura 
eritur in orbem rediens circiter circularis, que omnia monftrat annotina incrementa, 
extimo propemodum parallela. Fingamus jam talem feétionem in tenuem laminam com- 
preflam, et veram habebimus ligni foflilis, de quo heic agitur, ideam; nam in magnis 
hujus materiz fruflis, tranfverfim felis, quemlibet annotinorum orbium vifu perfequi 
ieet, ita plerumque coa€tum, ut duas lineas fere parallelas -exhibeat, quarum ‘extrema 
brevi 
