88 Mr. J. S. Bowerbank on Moss Agates 



within the boundaries of the tubes. In this state there are 

 rarely more than single gemmules following each other in 

 succession, but sometimes, although not often, the vessels ap- 

 pear to have been much enlarged in diameter, and the gem- 

 mules are then indiscriminately dispersed within its cavity. 

 In other cases they are considerably larger in size than those 

 we have just described, and exceed in their diameter the ves- 

 sel or its remains which accompany them, as if they had out- 

 grown and burst their natural boundaries, or that the partial 

 decomposition of the walls of the vessel had reduced its size 

 beneath that of the globular bodies contained within it. From 

 the structure of this series of vessels and their contents, and 

 their close resemblance in every respect to those which I have 

 described as being contained within the large sponge-fibres in 

 the former case, there can be but little doubt, that whatever 

 may have been their nature and purpose in the living animal, 

 they are at any rate the same tissue, but under somewhat 

 different circumstances. 



I have examined a considerable number of cut and polish- 

 ed specimens of Egyptian jaspers : they consist of numerous 

 layers of various colours, which are generally concentric, but 

 not always so ; for it is frequently evident that the manner in 

 which the material forming the layers was disposed has been 

 suddenly changed, and the stratification has assumed a di- 

 rection which is nearly at right angles to other lines of the 

 deposit, as if the finely comminuted material had been washed 

 by small quantities at a time, and from different directions, 

 into the cavity which may have formed the mould which had 

 given the external shape to the mass. Upon examining po- 

 lished specimens of these pebbles with a microscopic power 

 of 150 linear, as opake objects by direct light, they are seen to 

 consist of finely comminuted granules cemented together by 

 a semi-transparent siliceous matter, very much resembling in 

 its appearance that state in which the silex exists in the 

 flints of the chalk and the cherts of the greensand formations. 

 These granules are usually of a light buff or brown colour, 

 irregular in their form, but varying very little in size ; and the 

 colouring matter with which we find the various strata of the 

 pebble tinted appears to exist in the cementing matter, and 

 not in the granules ; for there is always a considerable mix- 

 ture of light granules even in the darkest coloured bands of 

 the stone, and this form and mode of disposition in no case 

 appears to have been influenced by the varieties of colour. 



Amid this mass of agglutinated matter, in many cases there 

 are to be found imbedded hundreds of beautiful little forami- 

 nated shells of about the same size, and closely resembling in 



