634 



SCIENCE, 



[N. S. Vol. IV. No. 96. 



whatever, nor even any evidence wMcla 

 suggests, that on the whole the rate of waste 

 and sedimentation was more rapid during 

 Mesozoic and Palaeozoic time than it is to- 

 day. Had there been any marked difference 

 in this rate from ancient to modern times, 

 it would be incredible that no clear proof 

 of it should have been recorded in the crust 

 of the earth." 



It may, therefore, be inferred that the 

 rate of deposition was no nearer the more 

 rapid than the slower of the rates recorded, 

 above, and, if so, the stratified rocks would 

 have been laid down in about 400 million 

 years. 



There are other arguments favoring the 

 uniformity of conditions throughout the 

 time during which the stratified rocks were 

 laid down, in addition to those which are 

 purely geological and depend upon the 

 character of the rocks themselves. Al- 

 though more biological than geological, 

 these arguments are best considered here. 



The geological agency to which attention 

 Is chiefly directed by those who desire to 

 hurry up the phenomena of rock formation 

 is that of the tides. But it seems certain 

 that the tides were not sufficiently higher 

 in Silurian times to prevent the deposition 

 of certain beds of great thickness under 

 conditions as tranquil as any of which we 

 have evidence in the case of a formation 

 extending over a large area. From the 

 character of the organic remains it is known 

 that these beds were laid down in the sea, 

 and there are the strongest grounds for be- 

 lieving that they were accumulated along 

 shores and in fairly shallow water. 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 trilo- 

 bites, with their long delicate antennae per- 

 fectly preserved, proves that in one locality 

 (Rome, New York State) the tranquillity 

 of deposition was quite as profound as in 



any locality yet discovered on this side of 

 the Atlantic. 



There are, then, among the older Palaeo- 

 zoic rocks a set of deposits than which we 

 can imagine none better calculated to test 

 the force of the tides; and we find that they 

 supply evidence for exceptional tranquility 

 of conditions over a long period of time. 



There is other evidence of the perma- 

 nence, throughout the time during which 

 the stratified rocks were deposited, of con- 

 ditions not very dissimilar from those which 

 obtain to-day. Thus the attachments of 

 marine organisms, which are permanently 

 rooted to the bottom or on the shores, did 

 not differ in strength from those which we 

 now find — an indication that the strains 

 due to the movements of the sea did not 

 greatly differ in the past. 



We have evidence of a somewhat similar 

 kind to prove uniformity in the movements 

 of the air. The expanse of the wings of 

 flying organisms certainly does not differ in 

 a direction which indicates any greater vio- 

 lence in the atmospheric conditions. Be- 

 fore the birds had become dominant among 

 the larger flying organisms their place was 

 taken by the flying reptiles, the pterodac- 

 tyls, and before the appearance of these we 

 know that in Palaeozoic times the insects 

 were of immense size, a dragon-fly from the 

 Carboniferous rocks of France being up- 

 wards of 2 feet in the expanse of its wings. 

 As one group after another of widely dis- 

 similar organisms gained control of the air, 

 each was in turn enabled to increase to the 

 size which was best suited to such an envi- 

 ronment, but we find that the limits which 

 obtain to-day were not widely different in 

 the past. And this is evident, for the uni- 

 formity in the strains due to wind and 

 storm no less than to those due to gravity. 

 Furthermore, the condition of the earth's 

 surface at present shows us how extremely 

 sensitive the flying organism is to an in- 

 crease in the former of these strains, when 



