Notices and Extracts from the Minutes of the Geological Societj/. 419 



2, — Notice respecting the Matrix of the Brasilian Diamond. By H. Heu- 

 land, Esq. m.g.s. [Read May 16, 1823.] 



The diamonds imported into Europe from Brazil are almost always insu- 

 lated. A few are imbedded accidentally, and some artificiallyj in a conglome- 

 rate called in America cascalhao, which is of alluvial origin, and consists of 

 rounded pebbles held together by a ferruginous cement. The accompanying- 

 specimen, a small octaedral crystal, is the only one I have seen in its real matrix; 

 it is surrounded by cupreous arseniate of iron (scorodite), and lies in a cavity 

 of massive brown ironstone. It was found at Antonio Pereira, and is, I be- 

 lieve, the first diamond that has been found there. Mr. Caldcleugh, who is 

 acquainted with the spot, informs me, that this ironstone occurs in veins or 

 beds 25 feet thick, that it rests on chlorite slate, and may be traced to a great 

 distance along the mountain chain. Baron Eschwege, superintendant of the 

 mines, to whose kindness I am indebted for the specimen, in a memoir whicli 

 he has lately published on the geology of Brazil, says that it is accompa- 

 nied by micaceous iron ore and itabirite, by which is meant a compound 

 partially slaty, partially granular, consisting of two varieties of specular iron 

 ore, the common and micaceous, mixed occasionally with oxydulous iron ore 

 and quartz. The mountain from which this compound derived its name is 

 situate between Villa Rica and Sahara. It may be seen 10 leagues off, and 

 at a distance has the appearance of a falling tower. The brilliancy of its me- 

 tallic surface also catches the eye when some miles distant, and accounts for 

 the appellation given it by the Indians, in whose language the words Ita bira 

 signify the bright rock. 



3. — Notice accompanying Specimens from Porto Pray a in St. J ago, one of 

 the Cape de Verde Islands. Extractedfrom a Letter from Major Colebrooke 

 to H. T. Colebrooke, Esq. m.g.s. [Read January 2nd, 1824.] 



The town and fort of Porto Praya are seated on a tabular eminence (c) at 

 the extremity of a bay formed by the headlands (fZand/) with the rocky islet(e) 

 detached from the former. Between the town and each of the two promon- 

 tories, the valleys (6 6) intervene, and form a sandy beach. 



The cliff (/) exhibits a broad white surface halfway up, conspicuous at a 

 distance. This appearance would probably continue to the landing-place (a), 

 but the structure of the rocks lies concealed under fragments and undercliff. 



