Introduction. 3 



when the waters of the rivers are very low, and the rocks aie exposed, 

 the field work, or more correctly the river work, has been done duriny 

 such times. 



It has been objected that ray accounts of the structure of the 

 district are based mainly on the rocks exposed in the channels of the 

 rivers. But the reason for this is obvious — there are very few other 

 exposures of the country rocks. 



The rocks of the hills, as well as those in the valleys, aie almost 

 invariably covered by heavy forest growths upon great thicknesses of 

 clay and sandy clays, the results of the decomposition of the rocks 

 in situ, which more or less completely hide the geological structure of 

 the country. A geologist may walk for many hours along the trails 

 and paths which here and there lead through the forest and not see 

 any indications of what the country is. The rocks he will most 

 frequently meet with will l^e masses of quartz and of concretionary 

 ironstone. Very occasionally he will tind in ravines near the heads of 

 small streams and creeks natural sections showing the country rock. 



But during very dry seasons the beds of the rivers become exposed 

 over lai'ge areas, and their courses give excellent natural sections along 

 which the structure of the districts can be readily studied. The 

 scour of the river usually has removed the softer decomposing portion 

 of the rocks, and exctdlent representative specimens of them can be 

 easily obtained. 



The rocks collected during the journeys have been subjected to 

 petrographical and chemical examinations, and tlie general results are 

 recorded in the chapter dealing with petrography. 



Those desirous of studying the geological structure and petrograpliy 

 of the Guiana Goldfields in fuller detail than aj)pears in this Handbook 

 are referred to the following : — 



'• Rei^orts on the Physical, Descriptive and Economic Geology of British Guiana.'' 

 By C. B. Brown, F.G.S., and J. G. Sawkins, F.G.H. . " . . . 1875 



" Uber die Regionalen Veriinderungen der Goldlagerstatten " By Dr. Emil E. 

 Lungwitz ' . . 1899. 



" The Lixiviation of Gold Deposits by Vegetation and its Geological Importance " ; 

 "The Placers of British Guiana." By Dr. Emil E. Lungwitz, from the 

 Mimng Jonrnal, liuUatnj (tiid Cuiniiicroial Gazette ..... 1900. 



" Geologisch-bergmannische Skizzen aus Surinam." By G. C. du Bois . 1901. 



■' Beitrag zur Kenntnis der Surinam ischeii Laterit und Scliutzrindenbildungen." 

 By G. C. du Bois 1903. 



" Guide Pratique pour la recherche et rEx[)loitation de Tor en Guyane Fran^aise." 

 By Dr. Levat 1898. 



"British Guiana and its Mining Development." By E. G. Braddon, from The 

 Mining Journal, liailtcatj and Coitnncrctal Gazette ..... 1904. 



"The Geology of the North-Western District." F.y J. B. Harrison and H. I. 

 Perkins 1897. 



"The Geology of the North- Western District" (Part If., '"Petrology"). By 

 J. B. Harrison. With Notes on the Microscopic Structure of the Rocks, 

 by J. J. Harris Teall, M.A., F.P.S., etc 1898 



