530 abstracts: paleontology 



erite, pyrite, and arsenopyrite. They are commonly tourmaliniferous. 

 In certain deposits, as at Rimini, tourmaline is extremely abundant; 

 in fact, it occurs there in the same abundance that characterizes the 

 tin lodes of Cornwall. Three types of tourmalinic lodes with transi- 

 tions between them are recognized — lead-silver, copper-silver, and gold. 

 The predominant is the tourmalinic lead-silver, a type peculiar to the 

 region, so far as shown by the literature of ore deposits. The ores were 

 formed at high temperatures, and it is regarded as probable that the 

 ore-forming solutions were a final differentiation product of the granitic 

 magma. 



The ore bodies of post-Miocene age are essentially precious-metal 

 deposits. They are characterized by the tendency of the quartz gangue 

 to display a cryptocrystalline development, either flinty, chalcedonic, 

 or densely saccharoidal, resembling porcelain. Equally characteristic 

 is the thinly lamellar calcite of the gangue and its pseudomorphic re- 

 placement by quartz, forming a type of ore common in so many of the 

 late Tertiary gold fields of the Western States. In common with these 

 the tenor of the ores decreases abruptly below the 500-foot level. These 

 deposits are typically developed in the upper Miocene dacites of Low- 

 land Creek, but their analogues at Marysville have furnished the bulk 

 of the output. A, K. 



PALAEONTOLOGY. — Cambrian Holothurians. Austin H. Clark. 

 American Naturalist 47 : 488-507. August, 1913. 



Among the remarkable organisms described from the Cambrian of 

 British Columbia during the past year by Dr. Walcott were a number 

 which he referred to the Holothuroidea, the most extraordinary of 

 these being a pelagic animal called by him Eldonia ludwigi. As the cor- 

 rectness of the determination of these creatures as holothurians was 

 questioned in a review by Dr. Hubert Lyman Clark, the present author 

 was led to reply to his criticism for the reason that, as stated in Dr. 

 Walcott's original paper, it had been he who first suggested the possi- 

 bility that Eldonia might be a holothurian, tho he had not at the time 

 examined the other specimens. 



Dr. Walcott, Dr. Hubert Lyman Clark and the present author all 

 made independent investigations upon the material in question, and 

 the last mentioned was led to the following conclusions: Eldonia is a 

 free-swimming holothurian, and is most closely related to the species 

 of the family Elpidiidae. In body form alone does Eldonia resemble a 

 medusa; this general resemblance may therefore be safely disregarded 



