164 Geological Society : — 



48. The essential nature or principle of the movements appears 

 to be electro-chemical motion, i. e. definite motion directly produced 

 by electro-chemical action. 



49. To illustrate the action, I have constructed an apparatus 

 consisting of two pairs of electrodes of platinum foil and mercury, 

 suspended at opposite ends of two copper wires upon a central pivot, 

 and rotating in an annular channel tilled with dilute sulphuric acid ; 

 but the power was too feeble to produce revolution of the necessary 

 moveable parts : it was not more than sufficient to produce a manifest 

 tendency to motion. 



In conclusion, I beg leave to suggest a trial of the sudden starts of 

 the mercury by momentary currents as signals in electro-telegraphic 

 apparatus. 



GEOLOGICAL SOCIETY. 



[Continued from p. 86.] 



May 16, I860.— L. Horner, Esq., President, in the Chair. 



The following communication was read : — 



" Outline of the Geology of part of Venezuela and of Trinidad." 

 By G. P. Wall, Esq. 



The district examined by Mr. Wall extends from the 8th degree 

 north latitude to the sea, and eastward of the 69th meridian. It 

 includes the Serrania (as the mountainous region is termed) and the 

 Llanos or plains to the south. The Serrania is a portion of the 

 Littoral Cordillera, and is continuous with the main ridge of the 

 Andes ; to the east it extends into the northern part of Trinidad. 



The most ancient rocks in Venezuela consist of mica-schists and 

 gneiss, and compose the author's " Caribbian Group, h so called on 

 account of these rocks forming for a great distance the southern 

 boundary of the Caribbean Sea. This term was previously adopted 

 for the same series of mountain-rocks in Trinidad, where their 

 eastward extension had been already studied. These strata consist 

 of — 1st, a series of micaceous and siliceous schists, various in aspect 

 and constitution ; 2ndly, sandstones, coarse and micaceous, fine- 

 grained and without mica; 3rdly, shales, ferruginous, micaceous, 

 and carbonaceous. 



These schistose rocks are highly distorted. In the western por- 

 tion of the district they have a breadth of about 30 miles, and rise 

 to the height of 8000 feet ; to the east they form lower ridges and 

 a narrower belt. They are interlaminated with numerous irregular 

 bands of quartz. Evidence is not wanting of the segregation of the 

 quartz having been subsequent to the formation of the strata, but 

 previous to the disturbances that the schists have undergone. 



White and blue limestones, generally crystalline, but sometimes 

 compact, occur in the schists in Venezuela, but still more abundantly 

 in Northern Trinidad. Some of the schists are granatiferous ; and, 

 from the presence of smaragdite, they sometimes form an eklogite. 



Gneiss also is present, and is markedly interstratified with the 

 mica-schists. The transition is occasionally gradual; but more 

 usually it is sudden and abrupt. The gneiss sometimes assumes 

 the irregular structure of granite, but is still distinctly bedded. It 



