9 



them. Some vein* of a similar substance are vesicular. I believe, however, that I his appear- 

 ance Iuh resulted solely from ttnj iron contained isi Ihc.-w finriiom of (he rock. Close to 

 this is a hand, ubuul o 1 fct-t iu breadth, of vertical laminae liaU decomposed and with eruc- 

 tated projecting 1 edjjet, Internally it is composed of crumbling fiiUpir having minute scale* 

 of mica scattered ll i rough it. Towards the in r face the line is rust)' and some deep black 

 ■taint occur throughout, 



Jiwr the poo at the rock exhibit* [Treat variety in its composition even within a nmnU 

 eompmt One specimen has a greenirii grey sacchariod fcLspaltue base in which crystals of 

 quart* and ucfUft of mica arc spirinjjly disseminated. Another u somewhat similar, but the 

 base is a dark brownish grey. Tn o I tiers whitish felspar und black mica and J mrn blende 

 are unilwi in uLLlVrrnE pro portion s, cifiial and well separated j or more finely granulated 

 and mingled j so as, when the mica is absent , to approach to the character of a sycnitic 

 greenstones 



Amotifl (he other interesting examples of varying structure and corn posit ion at Ihc Point 

 there, are some sol id blocks of a rudely [5 lobular shape , with the rock in thfl spaces between in 

 foliae from MSlh to l-Bth of an inch thick. Adjoining theso are some blocks which , within 

 I Lun-uiit of a Tew fect ? change tn their appearance and compel Lion, passing from a black 

 dolcrUk rtK'-k into a well ertslaUiied eoTnpouivl hornblende and felspar (syenUic dole- 



rile) in which the former in great h in except, • — into a similar rock in winch the frUpar 

 greatly increases and which at one place ii intersected by a rlicmboidal network formed by 

 fchvpalhie veins crossing each oilier t — and , Lastly a into a whitish grey rock similar 

 lu ilia t □ round the fjlube* before noticed. The rryfilallitalion between the opposing convex 

 sides of adjoining blocks exhibits yet anolber andslUl more fifrorujly marked variety f becom- 

 ing 1 abruptly very coarse,, so that same- of the specimens which I took from the line of junc- 

 tion hare, on one rid*; cither a granite ns minulc in iu granulation as fine sandstone , 

 or a compact uulerito, and, on the other, cry^lal^ of frlspar and scales or mica of an un- 

 usually larifjc siic. 



A Little beyond the SB. an^lo there is a band of semidcenm posed rock about 2 feet 

 brand coiiKLKtinj of srn.ill globular and cuboidal hesses, from 3 En G inches in diameter,, of a 

 very fine grained (jranite or eurite imbedded in, and protruding from, yellowish while clay. 

 Tnc former are rem posed of minute micaceous and horn bkn die grains thickly disseminated in 

 q base of granular quart* and felspar. It so strikingly resembles line ground pepper t especial* 

 If after dccamposil ion has commenced, that it may be called pepper granite* 'Hie latter has 

 original ly been in great measure fefopnlhfc. 



At the SE. Point the slight superficial depressions marking divisional plmmes* the prin- 

 cipal fissures and cbosnifl, and the lonjjer sides of depurate ledges aro all in NE.-5W. 

 lines j or lines not dcvlatinrj far from these directions. The first have given rise (□ the 

 two last. The cohesion of I he rock at the divisional plane, originally least, is further 

 weakened by partial decomposition along that line. The alternations of temperature from 

 eipofnire to the ray* nf a hurninj frnri Rii^reeded by immersion under tho waves, and the 

 removal of support on either j-idc by the mechanical action of the tea, cause the rock to 

 split along the plane, and ihm a It^ure U formed. A ledge or band between two fii- 

 aua, mi. B. 



