On Carboniferous Diatomacece. 417 



of the coal formation Diatoms lived and formed a part of its flora, 

 offers us, it apj)ears to me, a most valuable opportunity of making 

 an observation of much greater import. 



However little any one may be accustomed to the contemplation of 

 nature, it is easy to recognize how the various organic types can to a 

 certain extent be modified by the influence of climate and other 

 circumstances under which they are living. Nevertheless, the effect 

 of such influences is so much less perceptible, and the consequent 

 modification so much slighter in proportion as the type occupies a 

 more elevated position in the organic scale. Now, although, when 

 disserting last year upon the structure of the Diatoms, and the various 

 parts and substances which compose them, as well as the marvellous 

 ornamentation to be admired in their valves, I allowed myself to be 

 carried away by enthusiasm for these wondrous organisms, so far as 

 to say 1 that " the Diatoms, far from being such humble little plants 

 as to deserve banishment among the lowest organizations of the 

 Vegetable Kingdom, have a far better right to be looked upon as 

 forms as noble in their structure and perfect arrangement as they 

 are marvellous for their minuteness," it is nevertheless true that, 

 organically considered, they must be acknowledged simpler than 

 and therefore inferior to the humblest mosses and vascular plants. 

 Nevertheless, who could have expected (on the supposition that 

 Diatoms have been growing from the time of the first dawn of life 

 upon the earth, in such enormously long evolutions of centuries, and 

 in the succession of ever new states of temperature and climate) 

 that they would not at least have been greatly changed ? All the 

 forms I have been able to observe amongst the few ashes of the before- 

 mentioned coal present such an appearance that the most practised 

 and sharpest eye could not detect the slightest difference between 

 them and actually living Diatoms. In outline, structure, shape 

 and number of the flutings, — in short, in all the peculiarities 

 which characterize the species that we meet with in a state of 

 actual vegetation, — the Diatoms of the Carboniferous and Palaeozoic 

 periods agree exactly. In such immeasurable succession of 

 centuries, organic life under this most simple and primitive form 

 since its appearance upon the globe (notwithstanding the tremendous 

 catastrophes which have altered the condition of its surface) has 

 not experienced the slightest change, and remains unaltered up to 

 our day : so true is it that upon each organic type Nature has im- 

 posed an immutable law which restrains it within its own limits. 



But the successful result I obtained from the examination of the 

 Liverpool coal, and the discovery of Diatoms contemporary with its 

 formation (thus conclusively proving the existence of Diatoms in the 

 Palaeozoic epoch), revived my desire to institute a similar research 

 through coal from other sources. Otherwise it might be questioned 

 by some whether the Diatoms found in the chip of Liverpool coal 

 had not simply adhered to it by accident, without being contem- 

 porary with its formation : as it might happen that Diatoms should 



1 See my note "On the Structure of Diatoms," Atti dell' Accad. Pont, dei 

 Lincei, Anno 26, 19 Gennaro, 1873. 



DECADE II. — VOL. II. — NO. IX. 27 



