1903.] NATURAL SCIENCES OF PHILADELPHIA. 399 



(5) All the rocks earlier than the intrusive veins, and even parts of 

 these latter, show extensive alteration and probable transformation. 



One purpose of this abstract is to recall the fact that we have proofs 

 of physical connection with the Western Continent of these outlying 

 islands, not only from the physiographic features ; drowned valleys ; sub- 

 merged plateaus; trend of conformation through the major axes of the 

 present detached islands ; palseontological analogy with South American 

 forms of hfe; etc., but, in addition to all these, the close petrographical 

 relationship of the crystallized and crystalline rocks and their con- 

 geners with those of the mainland. 



Note. 



A paper has just been received from Dr. Callaway (December 27, 

 1902) on the Plutonic complex of Central Anglesey,^ in which some very 

 curious resemblances appear between the central complexes of Anglesey 

 and Cuba, dissimilar as are the more recent mantles with which in the 

 two cases these nuclei are clothed. 



In 1880 Dr. Callaway, in entire accord with Dr. Hicks and many of 

 the non-official geologists of Great Britain as well as of our compatriot. 

 Dr. T. Sterry Hunt, had established the pre-Cambrian age of these 

 Anglesey rocks. In 1888 the Rev. J. F. Blake had confirmed a note 

 previously made by Dr. Callaway of the production of schistosity in 

 diorite by pressure. In the eastern district of Anglesey Dr. Callaway 

 considers felsite and diorite the materials out of which the gneiss was 

 made: "but ■s^'ith them is associated the well-known binary granite 

 (haphte) originally called Dimetian by the late Dr. Hicks. A fourth 

 variety .... is the quartz-felsite claimed by that geologist as 

 Arvonian. It forms a part of the same magma as the granite, and must 

 be carefully distinguished from c^uartzless felsite, into which it is some- 

 times intruded in dykes and veins." 



After dividing the diorite and its modifications into hornblende-gneiss, 

 decomposed diorite and chlorite-gneiss, micaceo-chloritic gneiss, and 

 kersantite and biotite-gneiss, he says of the felsite that he "has never 

 succeeded in obtaining a specimen in its original state," and in analysis 

 it is almost indistinguishable from Vom Rath's rhyolite of the Euga- 

 nean Hills, and from a rhyolitic obsidian from Medicine Lake. With 

 the above are associated crystalhne limestones, of which the origin, 

 according to Dr. Callaway, is chemical segregation and not sedimenta- 

 tion. 



^ Quart. Journ. Geol Soc, Vol. Iviii, 1902. 



