1*96.] Geology and Paleontology. 53 



" It is further apparent that gold deposits have been formed at dif- 

 ferent periods, though, by far, most abundantly in later Mesozoic times. 

 Some of these later veins may have been locally enriched by passing 

 through earlier impregnations in schist or old concentrations in the 

 sandstones and conglomerates of the metamorphic series, the gold con- 

 tents of which have, however, only been proved in isolated cases. 



" These considerations strengthen the belief that the origin of the 

 gold must be sought below the rocks which now make up the surface 

 of the Sierra Nevada, possibly in -ranis ic masses underlying the meta- 

 morphic series." (Bull. Geol. Soc. Am., Vol. 6, 1895.) 



Precambrian Sponges.— M. L. Cayeux has published a prelimi- 

 nary note on the spicules of sponges found in the Precambrian beds of 

 Bretagne. The author describes the different forms of the spicules, 

 gives their dimensions, the mode of fossilization, and the probable 

 causes for their fragmentary condition. The principal conclusions de- 

 rived by M. Cayeux from his researches are (1) numerous spicules of 

 sponges of various species are found in the Precambrian phtanite for- 

 mations of Bretagne, and (2) that all the orders of sponges with sili- 

 cious skeletons are represented in these formations. 



A resume of the facts ascertained concerning this interesting fauna 

 is given by the author as follows : 



" It is impossible not to be struck by the ensemble of the sponges of 

 the phtanites of Lamballe. Even excluding all the spicules which, 

 although they certainly are sponges, yet are too fragmentary for exact 

 identification, there remains an assemblage of forms which points to a 

 very complex fauna. 



" In the light of our present knowledge this fauna appears to be 

 composed of Monactinellidse, probably abundant, Tetractinellida?, rel- 

 atively rare, numerous Lithistidae, and a few Hexactinellidse. All the 

 orders of Silicea are represented. The branching off of the sponges 

 is then plainly as early as the base of the Precambrian of Bretagne. 



" The oldest beds in which any remains have been found belongs 

 to the Archean of Canada. M. G. F. Matthew has described Cyatho- 

 spongiat eozoica from the Lower Laurentian of St. John (New Bruns- 

 wick) and Halkhondrites graphitiferus from the Upper Laurentian of 

 the same region. 



" Cyathospongia ? eozoica may be a species of Hexactinellidse, and 

 Halichondrites graphitiferus must be referred either to Monactinellidaj 

 or to Hexactinellida?. The authenticity of these fossil sponges has 

 been put beyond a doubt by M. Hermann Rauff. 



