of the so-called 'Crystalloids' of the Chalk. 199 



Though the facts I have already stated appear to me conclu- 

 sive, yet it is of course satisfactory to find that, though rarely 

 seen to advantage, compound Coccospheres do really occur in 

 the chalk; and, indeed, I had seen and made a drawing of one 

 nearly ten years ago, without having properly understood its 

 nature. They, however, like the Foraminifera, appear to have 

 undergone much more decomposition in the chalk than in the 

 fresh mud of the Atlantic, which is only what might have been 

 expected. 



But, besides simple ovoid Coccoliths, and others modified 

 by various marks and apertures, there occur in chalk minute 

 bodies which are apparently somewhat related to them, but differ 

 from anything hitherto found in the Atlantic mud. As an illus- 

 tration of these, I refer to figs. 3 and 4 (magnified 800 linear). 

 Those like fig. 4 are similar to Coccoliths in being oval and 

 spoon-shaped, but show four marks, arranged in a cross, instead 

 of two, or a single elongated nucleus. When bodies like fig. 3 

 are made to turn about, the under side of the broad end is seen 

 to be like fig. 4, which is, in fact, so to speak, the ground-plan 

 of fig. 3. There are various forms of these curious objects, 

 which are obviously of organic origin, and may be described as 

 Coccoliths with a sort of spine growing outwards from the centre. 

 These spines are four-sided, are sometimes pointed, sometimes 

 end in a small cross, and sometimes extend into four well-deve- 

 loped wings. When the ovoid base occurs alone, either owing 

 to the spine having been broken off or never developed, it is 

 difficult to distinguish them from some varieties of Coccoliths, 

 or at all events to point out any essential and widely remote 

 difference ; and therefore, though I have not yet met with suffi- 

 cient evidence to prove it, I cannot help thinking that at the 

 Chalk period there was a form of Coccosphere in which the 

 Coccoliths were to a greater or less extent developed into small 

 spines. 



It is not easy to determine the extent to which these various 

 ovoid organic fragments serve to make up chalk ; but, like the 

 Coccoliths of the Atlantic mud, and to a very similar extent, 

 they and their fragments do certainly constitute a very material 

 proportion of the whole. If to them we add the more or less 

 entire and broken Foraminifera, and such particles as can be 

 shown to result from their decay and from the decomposition of 

 the shells of Tnoceramus, it appears to me that we are in a posi- 

 tion to completely account for the origin of the deposit. The 

 importance of the fact of thus being able to make out the true 

 nature of the so-called ' crystalloids' is, that we can no longer 

 doubt the almost entirely organic origin of chalk. Had they 

 been due to a kind of crystalline action, we might indeed have 



