lis 



a foot to i>Wrjl faihonn in diamMcr. Thc^c balls are sometime* composed of curved la- 

 mellar concretion*, which always include a harder central mas* or nucleus* The Bpices 

 hetweco the concralioiu are filled with rrrarxitc of a softer nature which decay* readily, and 

 Lhus leave* the harder central masse* heaped en each ether, or strewed abou[> Such Unapt , 

 or 1' urn ul L , have been c r ft? neoii'.ly desr.rihgd jis mlled inihfiia brought from a distance to 

 their present situation by the agency ef current* that formerly swept the mirfurc of the 

 earlli. Example* of this kind of structure occur in the idaad of Arran T Bohtfiiii , th* 

 Harts T the Fitehitlijcbirgn , and in other countries" (1). 



In i he Pafo Uhin rock* the laminar strut Lure is seen well definst end trasrui vocal. In, 

 the glebukr form it it as regular u that of t rap pea n rock*} and Mr. Sciori'j description of 

 some remarkable eiampldd of ihh structure in a rcsinutli trachyte or pi tchatoriK porphyry in 

 one of the I'nrtza Island* might be applied verbatim to same of the Putt* Ubin rocks, It 

 is not confined Co spherical concretion*^ however, for, ** we hate seen, it lumclirnci occurs 

 in rectilinear tones [1], or on the plane surface* of cubical masses (Z) r and,, at other places, 

 in irregular variously curved planes In these latter cases it It not Imp rotable that the 



nuclei arc spherical or hemi trjhcrical towards their centre*, and LIilL I hi: laminae only be* 

 gran to depart from thin form, as the eipaadiug nuclei approached each other and prevented 

 further L[jih'[iciLilcnt development. In cases it sh obvious that the upper partial^ of the! 



laminae have been decomposed and removed by meteoric or oceanic action, and, sometimes* 

 by both combined. Whether the nucleus in must of these ca*es where onJy the upper por- 

 tion is exposed bo wholly globular or paw internally into a cylindrical form I am not at pre- 

 sent able to say. 



In o paper of great interest upon the granitic mountain df the /Jfoeitfu and i|j isca of 

 rocks" read before the Berlin Academy of Science* on the l&ih December 1541, ajid of which 

 an a infract is [riven in the lira ti umber of [he Journal of the Geolog ccal Society ef London t 

 M, yu* Due it refers the external Mocks with which the mountain is covered and Che con- 

 rent rio laminar structure of granite bo&m in general, to contraction, of (lie mats on cooling 

 He jjitea this view a. grand application by suggesting that the body of ellipsoidal nranile 

 mountain* consist n t Like small base*, of concentric layers f each repeating I he form of the 

 mountain on a diminished scale , — the whole of thin structure resulting from the mecha- 

 nical operation of refrigeration* This utruelurc is well in. irked in the granites of Dtoon and 

 Cornwall > which have a strati tied appearance, the beds conforming la the surfaces of the 

 fcbisLose rocks when these ure superincumbent. Sir Fl. m u Recur considers I hat the laminae 

 or beds probably agree in form wifh lhat of ihe original surfaces of the granite mastc* afler 

 protrusion. He observed at gnu place alternating beds of a decomposed and hard granite , 

 and he thinks that the difference of original itmcture may be duo to a tendency of (he 



t\) Edinburgh Enrtjrl>ptidi* . r p I 11 p- Ill 



1 ti j /vh f. 8 A-c 

 (3j ^Nfs p, 10 Aw, 



(1) .rfnf* P. a. IS At. 



22** mi. 1&47. 



