52 The A7nerican Naturalist. [January, 



.probably from Mauritius. Its principal distinctive features are the 

 very small tympanic cavity and the backward prolongation of the 

 palatines and vomers, the latter forming a suture with the basisphe- 



noid. (Proceeds. Lond. Zool. Soc, Jan., 1891.) Two species of 



Procoptodon are described and figured by Mr. Lydekker in the 

 Quarterly Journal of the Geological Society, Nov., 1891. These fos- 

 sils are two mandibular rami, and they were obtained from the clay- 

 beds near Miall Creek, on the Northern frontier of New South Wales. 

 They have been referred provisionally to P. rapha and P. goliah. 



MINERALOGY AND PETROGRAPHY. 1 



Petrographical News. — The eruptive rocks of Velay, Haute 

 Loire, France, in the order of their age are basalts, trachytes and tra- 

 chytic phonolites, augite andesites, porphyrinic basalts, nepheline pho- 

 nolites and nepheline basalts. Termier, 2 who describes them, gives but 

 a few brief notes on each type. The younger phonolites form the lar- 

 ger part of the hill. They contain aegerine in light-green porphyritic 

 crystals, and in microlites. At the south-east of St. Pierre-Eynac are 

 tertiary clay slates cut by dykes of phonolite, whose tiny veins pene- 

 trate metamorphosed phases of the elastics, and are thus consequently 

 regarded as the agents producing the alteration. The rocks represent- 

 ing the first stage in the alteration consist of granitic debris, in which 

 secondary opal has been deposited around the feldspar and quartz frag- 

 ments. In some instances, in addition to the opal there have been 

 formed also secondary quartz and calcite, the former as a fibrous rim 

 around the grains. In more intensely changed phases, the slate is 

 traversed by veins of phonolite, whose contact with the sedimentary 

 rock is not visible, since on both sides of it the material of the phono- 

 lite has thoroughly impregnated the slate. On the other hand the 

 phonolite of the veins contains sphene, but no augite, while the normal 

 rock contains an abundance of aegerine, but no sphene. In the final 

 stage all the quartz of the slate has disappeared, and the rock is com- 

 prised principally of opal, serpentine and clay (halloysite ?), with pleo- 

 naste, colorless augite and hornblende as new products. The alteration 

 is thus a alicification. In other, more rare cases, it is a feldspathiza- 

 tion.— Hutch ings 3 has recently studied the material of which slates are 



1 Edited by Dr. W. S. Baj iterville Me 



2 Bull. d. Serv. ,1. 1. carte '(ii'o!. .■. I- ,- \,,. j;} ' 1S9( , 



3 Geological Magazine VII, 1890, p. 2>M and :{K;, aui II,. ]S!U p. 164. 



