268 GENERAL REMARKS ON THE Ciiap. XVI. 



qiient expansion due to the crystallization of the constituents 

 has forced the quartz and gold, still fluid, into the fissures 

 of the neighbouring rocks, and so formed the auriferous 

 quartz veins. These are only developed in the slate rocks, 

 which, when such veins occur, must be at no great distance 

 from granitic eruptions, either visible, or such as may be 

 inferred to exist.^ 



The chinchona forests which I examined in the Tambopata 

 valley are between lat, 13° and 12° 30' S. The elevation 

 above the sea, on the banks of the river, is 4200 feet, while 

 the loftiest crests of the mountains which overhang it on 

 either side attain an elevation of about 5000 feet. In the 

 preceding chapter I have given a general idea of the nature 

 of the climate throughout the year, and my stay was too 

 short to enable me to give any more detailed information 

 for most of the months ; but I did not fail to take careful 

 observations while I remained in the valley, which will 

 give an accurate idea of the climate during the month of 

 May. During the fom-teen first days of May the results were 

 as follows : — 



Mean temperature 69g ° Fahr. 



„ „ at 7 A.M 68 



„ „ at 3 F.M 71^ 



„ „ at 9 p.M 69 



Mean minimum in the night 62| 



Highest temperature observed . . . . 75 



Lowest „ „ .... 56 



Entire range 19 



Mean variation in the 24 hours .. .. 10| 



Greatest „ ,, .... 15 



Least „ „ .... 6 



Mean of the dew-point 61| \ 



„ „ at 7 A.M 61*9 I Dry bulb 



„ „ at 3 p. II 62*5 j as above. 



at 9 P.M 60-9 } 



' Quarterly Journal of the Geological Society, Feb. 1, lytiO, p. 59. 



