﻿Vol. 64.] PETEOLOGY AND PHYSIOGRAPHY OF WESTERlf LIBERIA. 313 



16. A jN'ote on the Petrology and Physiography 0/ Western Liberia 

 (West Coast of Africa). B3' John Parkinson, II.A., F.G.S. 

 (Read March 18th, 190S.) 



[Plate XXXY— Map.] 



I. Petrology. 



By the kind permission of Sir Harry Johnston, G.C.M.G,, I am 

 enabled to make the following brief contribution to the geology 

 of part of Western Liberia. The district described lies to the north 

 and north-east of Monrovia, in Montserrado county, and includes 

 the lower part of the basin of the St. Paul or Ding Eiver. These 

 notes are the result of a seven months' journey in the Republic. 



Taking the southern part first, it should be noted that garnet- 

 schists and various gneisses, for the most part greatly decom- 

 posed, are exposed in the neighbourhood of Wliiteplains and along 

 the Caresburg lioad. In typical specimens of the former collected 

 near Whiteplains, garnets are abundant, much cracked and very 

 irregular in outline. Flakes of biotite are common, quartz is 

 occasionally plentiful ; and the felspar is, at least partly, an acid 

 plagioclase. Phenocrysts are rare. Kyanite-schists are pro- 

 bably associated -with these rocks, for the distinguishing mineral is 

 common in the gravels of the streams, but it has not yet been 

 traced to the parent rock. 



These garnet-biotite-granulites or schists form a well-marked 

 group, probably distiuct from the commoner gneisses with which 

 they are associated. In the latter the occurrence of a monoclinic, 

 and possibly also of a rhombic, pleochroic pyroxene is worthy of 

 note. Quartz is common, and occurs typically in elongated 

 len tides. 



The Whiteplains garnetiferous rocks may be correlated with 

 others petrographically similar, found between Suen and Arthington 

 on the western bank of the St. Paul, and with garnet-graphite- 

 gneisses and tremolite-schists at the last-named settlement. 



iSForthwards as far as Marakorri, westwards to Takwema and 

 eastwards to Sanoyei, no similar rocks were found. 



The Arthington rocks are associated to the south, between that 

 settlement and Millsburg, with granitic orthogneisses and 

 with foliated hornblende-schists. The last-named are common 

 throughout the district described. 



I am indebted to Mr. P. T. Byrde, Assoc.P.S.M., for the 

 opportunity of examining some rock-specimens collected near 

 Grand Basa, and to the north of that port. They are comparable 

 with the rocks of Arthington and Whiteplains. 



From the neighbourhood of Basa itself comes a fine-grained 

 biotite-garnet-gneiss, from near Dieh's Town a chlorite- 

 schist, and from Mount Findly a garnet-hornblende-quartz 



