804 



the younger volcanic products and therefore thev have been iiniied 

 with them. 



c. old pyroxene-andesiles and basalts with their breccias and tnffs 

 (iniocene). What has been said snb // also refers to them. 



6. i/ou/it/ volcanic products, chiefly of (luaternarj a^e, also pliocene 

 and recent. They form the young volcanoes which have been formed 

 from the young-leitiary llirongh ihe ipiaternary period while some 

 of them are still active. 



The above goes to show thai Of many igneous rocks, that have 

 been classed among a certain group, the age is difficult to establish. 

 Recent investigations have yielded fresh data which prompted us to 

 study again the age of the several igneous rocks. 



Ad i. 



VfcRBEKK suggests the [Xissibility that some of these rocks are 

 mesozoic, without being able to adduce any evidence for his hypo- 

 thesis. According to him only some places show distinctly the presence 

 of pre-permian rocks, for example the island of Letti, where diabase- 

 breccias are believed to be superposed with permiau limestone with 

 crinoids. Moreover the peridotite of Ambon, as is proved by the 

 granite dykes, is older than the last-mentioned rocks, while the 

 granites themselves are believed to be of permiau age, as the sand- 

 stone formation of Ambon, to which permiau or anyhow young- 

 palaeozoic age was assigned, consists of debris of granite. 



We must contend that: 



a. the argument for a pre-permian age in the island of Letti falls 

 through, as the permiau limestones occur as blocks only, which may 

 have been brought to this place by overthrusts ^). 



b. It is not possible yet to determine the age of the sandstone 

 formation of Ambon, by the fossils which have been found in the 

 limestones that occur in the formation '). However, the facies is 

 very much like that of the upper-triassic-rocks of Ceram '), in the 

 neighbourhood of Ambon and we believe it to be of the same age. 

 Proofs of the pre-permian age of granites and peridotites are neither 

 afforded by sandstones built up of the debris of granites. Failing 

 any evidence for a pre-permian age we must draw attention to the 



') G. A. F. MoLENGRAAFF and H. A. Brouwer. De geologie van het eiland 

 Letti. Ned. Timor Exped. I .Jaarboek v. li. Mijnv/ezen. 1914. Verb. Dee) I. p. 28. 



«) K. Martik in Tijdschr. Kon. Ned. Aardr. Gen. XVI. 1899. p. 656. 



G. BoEHM. Ueber Brachiopoden aus einem alleren Kalkstein der Insel Ambon. 

 Jaarb. v. h Mijnwezen. 1905. Wet. Ged. p. 88. seqq. 



5) H. A. Brouwer. Geo!. Verkenningen in de oostelijke Molukken. Feestbundel 

 Prof. G. A. F. Molekgraaff. Verb. Geol. Mijnb. Gen. Geol. Serie III. 1915. p. 36. 



