274 Messrs. J. H. Cooke and A. S. Woodward. 



the same stimuli give rise to the same sensation. That certain pairs of 

 spectral rays, red and blue-green, for instance, produce grey or white is 

 quite another fact, and may possibly be explained in the following way. 

 All the pairs of spectral rays which together make grey or white 

 are far apart from each other in the spectrum, and are not present in 

 rays given oat by any saturated pigment. Thus red and green rays 

 stimulate the retina when any yellow object is observed, a pigment 

 which gives out, in addition, the blue-green rays, is of a pale whitish- 

 yellow. Thus, while pigments which give out red and green rays 

 appear more yellow, those which give out red and blue-green rays 

 appear less so and approach the primitive achromatic sensation. 



Without knowledge of the changes which actually take place 

 when light falls upon the retina, and before therefore the subject is 

 really opened up, scientific observers have brought forward complete 

 theories of vision. Both in the theory of Young and in that of 

 Hering the visual organ is " conceived " by them, and in the absence 

 of facts these theories can only be looked upon as tentative. In this 

 paper an attempt has been made to arrange new facts by the side of 

 old ones, in order that they may be understood the better. Beyond 

 the point at which it is possible to explain a subject in terms of what 

 we already know in physics and physiology, no progress has been 

 attempted. Such attempts have in other departments of physiology 

 proved too often unsuccessful to encourage effort in a subject the 

 threshold of which every physiologist will agree that we are only 

 about to enter. 



" The Har Dalam Cavern, Malta, and its Fossiliferous Con- 

 tents." By JOHN H. COOKE, F.G.S. With a Report 011 

 the Organic Remains, by ARTHUR SMITH WOODWARD, 

 F.L.S., F.G.S., F.Z.S. Communicated by HENRY WOOD- 

 WARD, LL.D., F.R.S., V.P.G.S. Received February 2, 

 Read February 23, 1893. 



(Abstract.) 



The Har Dalam cave is situated in the eastern part of the island of 

 Malta, near Marsa Scirocco Bay. The headlands around the bay are 

 composed of Lower Coralline Limestone, capped by Globigerina Lime- 

 stone. Numerous valleys intersect the land at right angles to the 

 coast line, forming small creeks and bays at their embouchure. 



The Har Dalam gorge, in which the cavern is situated, is a valley 

 of erosion which carries off the drainage of the land above, and was 

 no doubt excavated at a time when the rainfall of Malta was much 

 greater than at present. This is indicated by the heaps of rounded 



