813 



the adjacent islands. Veiy likely in j'oung-raesozoic time a new period 

 began of markedly violent igneous activity, which culminated in 

 the tertiary and persists even in our days. Traces of this new period 

 are scattered over a considerable part of the eastern archipelago. 



When subdividing tiie eruptive rocks of the Moluccas accoj-ding 

 to their relative age into the following groups : 



a young-palaeozoic to old-mesozoic igneous rocks 



b young-mesozoic to tertiary igneous rocks 



c' young-volcanic products, 

 we ai-e in a [)osition to distribute a large number of the known 

 eruptive rocks with complete certainty among one of these groups; 

 for many rocks the subdivision might be carried down still farther. 

 In every group the rocks might be subdivided again according to 

 their petrographic characteristics. .Some rocks, however, there are 

 that riiay be older than young palaeozoic, while a large number are 

 still known as boulders. Too little is known of them to establish 

 their ages. In this connection we can subdivide the eruptive locks 

 first of all according to their petrographic characteristics. However, 

 here again we meet with the difficulty that of a great many rocks 

 no or, at all events, no detailed descriptions are at our disposal, so 

 that we are not competent to judge of their structure and their 

 mineralogical properties; moreover we are entirely or partially 

 ignorant of the geological occurrence of many of them. For a clas- 

 sitication from a chemical point of view we are absolutely destitute 

 of sufficient information. 



We distinguish the subjoined groups: 



a. granitic to dioritic rocks 



f). gabbro-like to peridotitic rocks (with 

 part of the serpentines and diabases) 



c. foyaitic to theralitic i-ocks 



(/. rhyolites and quartz-porphyries, tra- 

 chytes and porphyries without quartz, 

 andesites and porphyrites with kerato- 

 phyres, alkalirhyolites, alkalitrachytes, 

 trachyandesites 



e. basalts, melaphyres, pikrites etc. (with 

 part of the serpentines and diabases). 



ƒ phonolites, loucite- and ne|)heline- 

 rocks, trachydoloi'iles, tephrites and ba- 

 sanites, melilitebasalts, limburgites and 

 augitites. 



Proceedings Royal Acad. Amsterdam. Vol. XXI. 



To each group should 

 be added that part of the 

 graniteporphyric and fine- 

 grained ecpiivalents and of 

 the aplitic, lamprophyric 

 and pegmatitic rocks, which 

 corresponds most with it 

 on the ground of the avail- 

 able data. 



53 



