CHAP. X.] CONTINUITY OF THE CHALK. 499 



the sea-bed, was here accompanied by a great abun- 

 dance of animal life. 



I can scarcely" regret that the space at my disposal 

 will not allow me to enter at present into the many 

 very important bearings of these physical investiga- 

 tions, for I am compelled to admit that I do not 

 place thorough confidence in our results. The obser- 

 vations and analyses were undoubtedly conducted 

 with great care and skill, but the difference between 

 different samples — in specific gravity, and more espe- 

 cially in chemical composition and the relative pro- 

 portion of the ingredients — is so very slight, that more 

 exact methods than those which have been hitherto 

 employed will be required to insure accurate results. 



In such investigations everything depends upon 

 the perfection of the means of bringing up water 

 from any given depth ; and the principle of the 

 construction of the water-bottle used in the ' Por- 

 cupine ' was faulty. It consists of a strong tube of 

 brass about two feet in length and two inches in 

 internal diameter, containing rather more than a 

 litre and a half, and closed at each end by a brass 

 disk. In the centre of each of these disks there 

 is a round aperture closed by a well-ground conical 

 valve, both valves opening upwards when the instru- 

 ment is in position for being let down. 



In passing down through the water, a continuous 

 current is supposed to raise the valves and run 

 through the bottle, thus keeping it constantly filled 

 with the water of the layer through which it is 

 passing. On reversing the motion in hauling up, 

 the valves fall into their places, and the contents 

 of the tube at the greatest depth are brought to 



K K 2 



