Rev. 0. Fisher — On Dynamo-Metamorpkism. 



303 



referred to is of interest as it serves to strengthen the resemblance 

 of the English Pliocene Echinoidea to those of the West Indian area. 

 The close connection between the echinoid faunas of the Tertiary- 

 deposits of the Antilles and of the Mediterranean subregions has 

 been frequently insisted upon, notably by Prof. Al. Agassiz. 1 Hence 

 the resemblances noted by Forbes between the Crag species and 

 those now living in the Mediterranean do not diminish the more 

 intimate connection of the former with the present West Indian 

 fauna. 



As far as can be judged from our present knowledge of the recent 

 and fossil distribution of Rhynchopygns, it lived in the seas of the 

 Palaearctic region from the Cretaceous to the Pliocene ; about the latter 

 period it migrated westward, for B. Woodi is apparently the last 

 European representative, and it does not seem to have been recorded 

 from the rich faunas of the West Indian Miocene. It now survives 

 only round the shores of the Mexican and Antillean subregions of 

 the Neotropical region. The genus is in fact confined to the littoral 

 zone of a tropical sea, and it is difficult to see how it could have 

 crossed the deep and cold abysses of the Atlantic. Hence either 

 the European Miocene and Pliocene Echinoidea must have migrated 

 westward along a belt of the continental zone that then stretched 

 across the temperate regions of the Atlantic ; or, the Echinoid fauna 

 of the West Indies and the European later Tertiaries must have both 

 originated from one that occupied an area of comparatively shallow 

 sea somewhere in the North or Central Atlantic. 



V. — On Dynamo-Metamorphism. 

 Bythe Rev. 0. Fisher, M.A., F.G.S. 



I HAVE derived much help towards understanding Mr. Harker's 

 instructive letter upon the above subject from making the 

 following simple geometrical construction. 



D C K F 



Suppose A B G D to be the section of a cube of the contorted 

 rock. 



For simplicity we may suppose that the contorting pressure P has 

 been met by a fixed abutment at A D. Suppose that in the process 

 the mass B C F E has been forced past B G, and that the result 

 1 " Challenger," Rep. Zool. vol. ii. p. 30. 



