G. W. Bulman — The Geological Chronometer. 123 



of the tides ; and we find that they supply evidence for exceptional 

 tranquility of conditions over a long period of time." 



But, we ask, would the existence of higher tides necessarily 

 destroy this appearance of tranquility ? There is, so far as I am 

 able to grasp the facts of the case, no grounds for suppostng that 

 higher tides would prevent tranquility of deposition. But we can 

 put the matter to the proof. We have deposits which have been 

 laid down in lakes and inland seas where there are no tides. Do 

 these show the marks of tranquil deposition — whatever these are — 

 to a greater degree than those of the open ocean ? Would any 

 geologist be able to distinguish the deposits of the Mediterranean 

 as having been laid down under more tranquil conditions than 

 those of the Atlantic ? 



As regards the extremely delicate organisms which, Professor 

 Poulton remarks, are found in the Silurian, it is difficult to realize 

 how a higher tide would affect them. And it is not quite clear 

 whether it is the fact of these delicate organisms having lived or 

 their having been preserved which is supposed to show that the tides 

 were not appreciably higher in Silurian times. Professor Poulton's 

 exact words are : — 



" The remains of extremely delicate organisms are found in immense- 

 numbers, and over a very large area. The recent discovery, in the 

 Silurian system of America, of trilobites, with their long delicate 

 antennse perfectly preserved, proves that in one locality (Rome, 

 New York State) the tranquility of deposition was quite as profound 

 as in any locality yet discovered on this side of the Atlantic." 



If the higher the tide the less delicate the organism capable of 

 living in the water, then the organisms of the Mediterranean ought 

 to be more delicate than those of the Atlantic. Here, then, we can 

 appeal to facts. As the question is outside the scope of my knowledge 

 I must leave it in the form of a query. But, so far as my geological 

 knowledge carries me, the fossils of lake and inland sea deposits are 

 not of more delicate organization than those found in the strata of 

 the open ocean. 



And if the finding of a few of the "long delicate antenna" of 

 trilobites in America proves the profoundness of the tranquility, 

 what does their universal absence in this country show ? Again, 

 there arises the question of the relative delicacy of the organisms 

 of the Silurian. Have we the right to say they are as delicate as 

 some of the organisms of our present seas? Can we, for example, 

 really say from what we know of their remains that the graptolites 

 were not able to stand more tossing about — assuming for a moment 

 that higher tides would make it more tempestuous — than the 

 Sertidaria of our present seas ? The chitinous rod of the graptolite 

 may have been very tough and strong. We have no means of 

 measuring its strength. It must be left an open question whether 

 or not it was fitted to live in a more stormy ocean than the present. 



Again, Professor Poulton says : — " Thus the attachments of marine 

 organisms, which are permanently rooted to the bottom or on the 

 shore, did not differ in strength from those which we now find, an 



