PHOTOGRAPHY. 341 



seen, some have differed so little in colour from the attached 

 rock which formed the ground, that the representation of 

 them hy photography in the ordinary manner was most 

 unsatisfactory. In many instances the natural irregularities 

 of the surfaces of the ohject were of far greater value in 

 assisting in the determination of it than the contour and 

 markings defined by the local colour, and such objects when 

 copied as stereographs were rendered in a much clearer 

 manner. 



The practical details of the photogra])hing of some of the 

 above, and of the systems of illumination and development 

 adopted are most interesting. The working out of these and 

 the results of the many experiments made in order to secure 

 the best rendering of each specimen were also exceedingly 

 instructive, but a description of them would scarcely lie 

 within the province of a paper read in this Section, and, 

 indeed, would be of little value without practical demonstra- 

 tions, convenience and time for which do not exist. 



Instances (such as the one quoted) in which the great use 

 of the stereoscope is evident might be multiplied indefinitely, 

 and in everyday work there are very few subjects which do 

 not absolutely demand it ; for this reason its value cannot 

 well be made too prominent, and every geological photograph 

 of natural scenery should be stereoscopic. 



For those who object to the small size of the ordinary 

 stereoscopic print the reflecting stereoscope is recommended, 

 as the size of the prints which may be examined therein is 

 limited only by convenience. 



The photographing of all important rock sections which 

 are exhibited by railway or other cuttings, or by landslips 

 and excavations, as well as all fossils, should in most cases be 

 executed as soon as possible after the excavations have been 

 made or the fossils discovei'ed ; some of the latter begin to 

 alter in appearance directly they are exposed, and many 

 commence to decay or decompose very shortly after. Sec- 

 tions brought to light by excavations also often become 

 completely changed by atmospheric and other influences 

 very quickly, and the differences in colour of the various 

 strata, though not always most marked when the surfaces are 

 new, are very often so. Under any circumstances the first 

 shower of rain introduces foreign matter, and otherwise 

 alters the state of things. 



In the paper read by the author at the Melbourne meeting 

 an attempt was made to point out the lines upon which the 



