404 



Profs. V. A. Horsley and E. A. Schafer. [Dec. 10 r 



present this member of the series is only seen as a number of isolated 

 patches, and we have no evidence as to whether it ever constituted a 

 continuous deposit. Its thickness is never great, and probably in no- 

 case exceeds 30 feet. 



The " Cherty rock of Stotfield " which has afforded no traces of 

 organic remains, even when studied under the microscope, is evidently 

 a chemical and not an organic deposit. Its appearance and characters r 

 indeed, strongly suggested that, like very similar deposits in Hun- 

 gary, it may have been formed by geysers, an idea which was 

 entertained by Sir Charles Lyell. If this be so, it is impossible to- 

 avoid entertaining the suggestion that the formation of the keys may 

 have been due to the rise of heated water containing silica in solution 

 along the joint planes of sandstones below. Some support is afforded 

 to this suggestion by the fact that where, as at Stotfield, the Cherty 

 rock is largely developed, there the quartzite " keys " are particularly 

 numerous in the underlying sandstones. 



It may be of some interest to add that the Trias of the district of 

 Scania in Southern Sweden contains rocks quite undistinguishable in 

 their mineral characters from the Pebbly Conglomerate, the Repti- 

 liferous Sandstone, and the Cherty rock of the Trias of Eastern 

 Scotland. 



V. " Experimental Researches in Cerebral Physiology. II. On 

 the Muscular Contractions which are evoked by Excitation 

 of the Motor Tract." By V. A. Horsley, M.B., B.S., 

 Professor Superintendent of the Brown Institution and 

 Assistant Professor of Pathology in University College, 

 London, and E. A. Schafer, F.R.S., Jodrell Professor of 

 Physiology in University College. Received December 1, 

 1885. 



The following note gives the results of a large number of experi- 

 ments which we have undertaken, in order to determine the character 

 of the muscular contractions which result from excitation of the several 

 parts of the motor tract, especially with reference to the rhythm 

 with which the skeletal muscles respond to such excitation. 



For the purpose of our experiments we may consider the motor 

 tract under four heads, viz.: — 1. Its commencement in the nerve- 

 cells of the cerebral cortex. 2. The connexion of these cells with 

 the lower nerve-centres by the nerve-fibres in the corona radiata. 

 3. Its continuation along the medulla oblongata and medulla spinalis 

 (including the nerve-cells of those structures). 4. Its peripheral con- 

 tinuation along the motor nerves. 



