TRACKS OF INVERTEBRATE ANIMALS. 25 



production of ripple-marks, and a subsequent sculpturing 

 by drainage-currents. The ripple-marks, at the point in 

 question, curved diagonally across the lines subsequently 

 followed by the drainage-streamlets. Hence the surface 

 of the sand was cut up into the very regular, diagonally 

 arranged, contours represented in Plate III. fig. 14. We 

 have here two sets of regular ripple-marks, one of which 

 passes from the upper to the lower margin of the figure, 

 from right to left. A second and more sharply defined set 

 crosses these diagonally, i. e. from left to right. These 

 lines were, of course, formed under the water. When 

 the tide had retreated sufficiently, drainage-lines began to 

 form ; but these pursued their direct course down the 

 sloping sand-bank towards the sea. The result of this 

 triple action was the formation of a series of regularly 

 arranged, acuminate contours, the surfaces of which were 

 characterized by longitudinal flutings, resembling the over- 

 lapping scale-leaves of some Cycadean stem. They readily 

 might, and probably would, have been mistaken for such, 

 had they been discovered on some slab of Oolitic sandstone. 

 Fig. 15 exhibits a slight difterence from fig. 14. Here 

 we had only one diagonal series of ripple-marks, followed 

 by the formation of drainage-lines as before. The result 

 is an eff'ect not unlike that of two or three corrugated 

 Laminarian fronds overlapping one another. 



I have no doubt that further investigation will bring to 

 light other examples of inorganic configurations simulating 

 organic forms. I am somewhat surprised that so little 

 attention has hitherto been paid to the results of littoral 

 drainage-lines. Sir J. W. Dawson figures an example of 

 one such result, but of very different aspect from those 

 now described, in his memoir on tracks of Invertebrata 

 in Silliman^s American Journal, entitled " On the Foot- 

 prints of Limulus as compared with the Protichnites of the 

 Potsdam Sandstone" (1862). But I have not met with any 



