16 Geology of the Gold Fields of British Guiana. 



The sandstones of this range form mountain-caps, and terraces on 

 the slopes, which rest on igneous and metamorphic rocks. 



The part of the range of the Imataca Mountains, situated on the 

 western extremity of the North-Western district of the colon)' rises 

 fi'om 800 to 1,500 feet above sea level, and divides the waters flowing 

 to the Orinoco and Cuyuni rivers from those of the Amacura, Barima 

 and Barama rivers which flow directly to the Atlantic Ocean. The 

 watershed on this range extending from the source of the Amacura 

 around the source of the Barima to the source of the Akarabisi, forms 

 part of the western boundary of the colony with Venezuela. These 

 mountains consist of igneous rocks, principally granite, (juartz- 

 porphyry, felsite, porphyrite and diabase, and are entirely forest-clad. 



Lower spurs of this range extend eastwards beyond the source of 

 the Waini lliver ; and others reach as far as the Essequibo estuary, 

 where they give rise to the Groete Creek and tributaries, and are 

 known as the Blue Mountains. 



The Kanuhih Mountains. — Rising above the plains to the south 

 of the Pakaraima Group are the Kanuku Mountains, none of which 

 exceed 2,000 feet in height above sea level. The range commences at 

 the Takatu, and continues in a westerly direction to the Rupununi 

 River and beyond it as far as its tributary, the Quitaro, dividing the 

 elevated savannah into two nearly e([ual parts. The Kanuku 

 Mountains are entirely forest-clad. 



Ranges and Mountains of Less Importance. — Of the smaller 

 irregularly distributed ranges of mountains the following may be 

 noticed : — The Maburima or Aruka Hills, near the Aruka River, 

 which are the nearest hills to the coast, the Arisaru Hills, which 

 extend from the lower Essequibo River to the Demerara River, their 

 altitude being about 800 feet, the Maccari, between the Essequibo 

 River and the Berbice River, and the Makarapan near the mouth 

 of the Rupununi River ; the two ranges last mentioned, although 

 detached, are really outliers of the Pakaraima Range. 



To the south of the above are the smaller ranges of Tamutan and 

 Kusaad, situated between the Takatu and the Rupununi Rivers. 

 Further south are the Karawaiming Mountains, in the vicinity of 

 the source of the Quitaro River, and the partly grass-clad Ussari Moun- 

 tains, which are near the source of the Kassi-kidju ; both of these are 

 unexplored. The most notable of the many isolated mountains are 

 Sheriri, Piniette, Shuna, Wamuriak-Tawa and Win Tawa. The main 

 sources of the Takatu River are in the two last-mentioned. 



It may be observed that, in conformity with the general distribution 

 of heights which obtains in the two continents of America, the greatest 

 heights are on the western limits of British Guiana, and that both the 

 mountain ranges and the general level of the country diminish in height 

 as they extend eastwards. 



