200 Description of the Psittacus Fieldii, 



able grass-green, in some lights tinged with golden yellow, and 

 in others with brown. The under plumage is paler and more 

 inclined to yellow. At the base of the wings, adjoining the sca- 

 pulars, there is a small obscure reddish spot. The quills on their 

 outer surface are dark green, but on the inner surface dusky 

 black ; while the inner wing-covers, and the feathers on the sides 

 of the body immediately adjoining them, are of a brilliant sky- 

 blue. The second and third quill are very slightly longer than 

 the first. The tail is of a moderate length and rounded, and the 

 extremities of the feathers are ovately or obtusely pointed : the 

 colour above is green, with the interior webs yellowish ; and this 

 last colour predominates on the under surface. The tarsi are 

 black, and comparatively short. 



Art. IV — On the Origin, Materials, Composition, and Ana- 

 logies of Rocks, by John Mac Culloch, M.D,, F.R.S.E. 



[Concluded from p. 44.] 



Of the Analogies among different Rocks, and of their resemblances 



to Unconsolidated Strata. 

 Having thus attempted to assign probable causes for the conso- 

 lidation of the original materials of rocks, it will not be useless 

 to attempt to trace these through their progress; to inquire 

 if it is possible to discover, in the component parts and disposition 

 of the most ancient rocks, any resemblance to the loose matters 

 which are now daily deposited beneath the waters of the present 

 earth. 



On the subject of the unstratified rocks, little can here be said 

 in addition to the remarks on their origin which have often been 

 made ; but as these must have been formed out of previous rocks, 

 and not from original materials, it will be better to postpone any 

 observations on them till the last. 



If we examine the deserted seat of an inland lake, we discover 

 beds of compact mud intermixed with leaves, or of mud with land 

 shells, or of sand, or of peat, or of all these, in one or more series 

 of alternations. Abstracting the question as it relates to peat, 



