IN BORNEAN FORESTS [chap. 



of the minerals and ores. Accordingly, when I felt a little better, 

 I started for Busso, going along the same route I had followed on 

 a previous occasion, and thence proceeding to Grogo. 



The geological formation of the Grogo mountain had a special 

 interest for me, and I was able to ascertain that it is of a crystalline 

 and eruptive nature, like that of the Pinindjao and Singhi moun- 

 tains. So, at least, say the notes I made on the spot in my journal. 1 

 I collected specimens of the rocks in order to have them more care- 

 fully examined on my return to Europe by some competent special- 

 ist, but, unfortunately, they were lost, together with most of the 

 other rocks and minerals I had collected in Borneo. 



Singhi, Pinindjao, Grogo, and, I believe, Sunta, which, however, 

 I did not visit, are the only examples of crystalline and eruptive 

 geological formations found in the vicinity of the antimony mines. 



At Grogo amongst the more remarkable plants which I met I 

 may mention a Costus, with a fine orange-yellow flower, borne on a 

 short radical stem. On the cliffs, in the most inaccessible places, 

 I observed a lot of honeycombs, which I think belonged to the same 

 species of bee which usually resorts to the tapangs. The Grogo 

 Dyaks brought me several specimens of a bivalve (Alasmo- 

 donta V ondembuschiana) which lives in the streamlets near their 

 village, and which not infrequently contains small pearls. From 

 Grogo I went through Busso to Paku, to examine the alluvial forma- 

 tions from which the Chinese extract gold ; and from them I bought 

 samples of the auriferous sand. Gold is also found on the bottom 

 of caves, in isolated particles, or adhering to the sides and jammed 

 into the fissures of the limestone rock. I was able to get some good 

 samples of this peculiar auriferous formation. 



It has been thought difficult to account for the presence of gold 

 in caves, and in the neighbouring limestone rocks, but to me the 

 explanation appears an easy one. I have previously remarked how, 

 in the Busso district and in that of Bau (where gold and antimony 

 are found), isolated peaks rise up from the plain, formed of cavernous 

 limestone, which I believe to be of madreporic origin, and thus of 

 slow submarine formation. Moreover, the vicinity of mountains 

 formed of eruptive rocks (like those mentioned above) in the same 

 districts with the limestone hillocks, would point to volcanic action 

 having taken place in the same sea that witnessed the madreporic 

 origin of these limestone hills. Under such circumstances the dis- 

 engagement of sulphurous gases was probable, and how these may 

 have formed chemical combinations with the antimony, the arsenic, 

 and the mercury which occur in the same area is easily imagined. 

 The sulphurets thus formed would crystallize in the fissures and 



1 The compact soil, of a clayey aspect, often perfectly white and similar 

 to kaolin, which forms the hills of Kuching, appears to me to be the product 

 of the decomposition of the rock of which these three mountains are formed. 



352 



