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of undoubtedly local blocks, which, petrographically, should 

 represent all the most important varieties. The appearance 

 varies very considerably, even if the main mass consists of 

 moderately acid porphyries. As for the many divergent forms, 

 it is, unfortunately, impossible as a rule to decide whether they 

 are formed as a kind of endogenous magmatic precipitations, 

 or whether in this case there have been several different epochs 

 of eruptions. 



That to some extent at least, the latter has been the case, 

 is indicated by some dikes of dark rock which were observed 

 to penetrate the sedimentary beds. I shall describe them 

 below; at least one of them, a true basalt, is presumably much 

 more recent than the remaining rocks. 



We will pass on to a description of the various main types 

 that I saw on the spot. 



a. Coarsely crystalline, syenite-like rocks. In the material 

 collected, we come across a single specimen of a plutonic 

 rock, macroscopically a deep-red granite without anything espe- 

 cially peculiar in its appearance. Microscopically, however, one 

 can see that the quartz occurs exclusively as rounded, sharply 

 defined aggregates, often surrounded by or in close connection 

 with areas rich in chlorite and of an appearance that is foreign 

 to the ordinary mass of the rock. It is not easy to decide if we 

 are in the presence of remains of an older rock, destroyed by fusion, 

 or secondary secretions in a kind of miarolitic cavities. For 

 the rest, the rock consists of large individuals of strongly red- 

 dened orthoclase, which embraces small fresh crystal individuals 

 of plagioclase. However this rock may have originated, it is 

 evidently no normal plutonic rock; undoubtedly it must be re- 

 garded as a local type, closely related to the following sur- 

 face rocks. 



b. Acid orthoclase-b earing porphyries. The specimens in 

 this case derive to a large extent from the above-named dikes 

 in situ, which, already macroscopically however, show great 



