COMPOSITION OF THE SAND. 149 



The results of the analysis are as follows. Three samples of 

 dredgings, obtained from Mr. E. Jackson, M.I.C.E., Port Engineer, 

 Karachi : — 









D 



redgings. 











No. 





No. 



No. 





Samples 





1. 





2. 



3. 



Mean 



Left on sieve No. 



10 



6-o 





9-0 



... 



5"o 



99 



24 



3'5 





8-5 



... 



4'o 



J» 



5° 



10*0 





24o 



6-o 



i3'5 



19 



70 



27*0 





38-5 



46-5 



37'3 



91 



100 



34"5 





1 8-o 



37-0 



20/S 



Passed through 



100 



1 0/0 





1 '5 



10-5 



10*4 



No information accompanied these samples as to the portion of the 

 harbour from which each was derived, but they were sent as fair sam- 

 ples of the material dredged from the harbour, and the mean of the 

 three may be taken to represent approximately the average composi- 

 tion of the dredgings removed from the harbour. 



As may be seen from the analysis, the three vary considerably in 

 nature. That numbered 2 appears to be from the outer harbour ; the 

 coarser fragments are all pieces of shell, and fragments of shell form 

 the greater part even of the finer sand ; this, and the absence of fine 

 silt, point to its being material which has travelled round the Manora 

 Point and been washed into the harbour. 



The sample No. 1 is not very dissimilar to No. 2, but the fragments 

 of shell do not seem so large, and a proportion of the coarser-grained 

 material is composed of cinder and coal, showing that this sample was 

 obtained from within the harbour, where ships can anchor and coal. 



Number 3 is of a totally different character to the other two : it is 

 comparatively free from shell-sand and is composed for three-quarters 

 of its bulk of fine sand. It must be remembered that in the process of 

 dredging there is a tendency for the finest-grained clayey matter to be 

 washed out to a great extent, but this dredging contains lumps of fine- 

 grained silt, evidently forming part of the original bottom of the harbour 

 in the state in which it was before being dredged. It seems clear that, 

 while the first two samples consist largely of matter drifted into the 

 harbour, sample No. 3 consists of part of the original bed of the 

 harbour, whether of tertiary or recent age, which has been dredged 



( 17 ) 



