238 



exception. Parts of tlie skeletons of sponges have also l)een clianged 

 into chamosite in these rocks. 



Another sandstone of the same finding-place is more compact 

 and contains mnch less calcite. Microscopically it appears to consist 

 of angnlar and rounded quartz-grains, the intervening spaces of which 

 are filled with fragments of sponges, the skeleton parts of which 

 have been altered into chamosite. Oolitic formations are scarce. 



In connection with the rocl<:s described above attention must 

 be paid to a limestone that was found in the Wai Najo in bank- 

 shaped flakes. The greenish grej fine-grained rock leaves at the 

 solution in hydrochloric acid a green sandy residue which appears 

 to consist of quartz and chamosite, the latter at the same time as 

 petrifaction-material of numerous skeletons of sponges. In the thin 

 sections of the rock the grains of calcite show rhomboedrical cleavage 

 and form partly also polysynthetic twins. They likewise enclose 

 [)articles of chamosite. Oolitic formations are not rare, but in this 

 case only the outer zone consists of chamosite, whilst the inner 

 part is still calcite, in which the rhoniboedric cleavage-planes of 

 the neighbouring grains of calcite have found their immediate con- 

 tinuation, so that they form with these one individual. The skeletons 

 of the sponges have been metamorpho.sed into pui'e green chamosite, 

 whilst the intervcjiing spaces are filled with lim[)id calcite. Besides 

 the constituents mentioned numerous quartz-grains arc present. From 

 the above it appears that the limestone contains the same constituents 

 as tlie sandstones that contain chamosite, and that there exists only 

 a quantitative difference. 



As regards the formation of oolites, there can be no doubt that 

 they have come into existence in the still soft mass of rock during 

 or after the sedimentation. In my opinion they have originally con- 

 sisted of carbonate of lime. That chamosite is no original mineral 

 is already proved by the metamorphosed parts of the skeletons of 

 sponges. It remains still unexplained which chemical processes have 

 operated to bring this metamorphosis about. E. R. Zalikski has given 

 an excellent summary of the different theories regarding the formation 

 of thuringite and chamosite ^), but it appears that none can be regarded 

 as valid. 



Finally a few annotations about crystallized minerals of Taliabn 

 may follow : 



Fyrite occurs — as has already been mentioned — in the shape 



1) Untersuchungen iiber Thuringit und Chamosil aus ïhüringen und Umgebung. 

 Neues Jalnb. f. Miner. Beil. Bd. 19. 1904, p. 79—82. 



