98 REPORT — 1855. 



which various structures are produced, for which the author proposes the general 

 term " current structures." The first of these is when the beds are deposited in 

 horizontal bands, indicating httle or no current at the bottom. The second has 

 been known by the term " ripple marking ;" but a very careful study of it yields 

 far more information than would be expected at first ; for, by carefully attending 

 to the peculiarities of its structure, the direction and velocity of the current can be 

 very generally determined, and even the actual rate at which deposition proceeded. 

 The third kind of structure has often been called " false bedding;" but for this the 

 author proposes the term " drift bedding." This furnishes information respecting 

 the direction of the current, but not necessarily the velocity. However, by carefully 

 attending to minute facts in its structure, it appears almost certain that the actual 

 depth of the water can in many cases be ascertained to within a fathom. By means 

 of these various structures, the direction of the currents can be made out with great 

 accuracy, as well as their general characters ; whether they were oscillating and due 

 to tides or stranding waves, or moved only in one direction. Thence the peculiari- 

 ties in the motion of the currents from which the physical geography of the modern 

 seas might be inferred, would permanently impress these characters on the deposits 

 formed in them, in such a manner that similar inferences might be derived from the 

 study of our ancient rocks. 



Applying these general principles to particular cases, it was shown that the red 

 sandstone of the valley of the Annan at Moffat was accumulated by ordinary tidal 

 influence in a small maiine loch. The detailed structure of the magnesian lime- 

 stone in the south of Yorkshire proves that the tide moved in a line from S. 70° W. 

 to N. 70° E., amongst a number of shoals. There must have been a much more 

 open sea towards the east than the west, because the greater storm-waves come from 

 that quarter ; but yet they were never very great, as might be expected in a sea that 

 was generally shallow and full of shoals. The Wealden also has such a structure 

 as agrees with the rise and fall of the tide amongst a number of sand-banks, like 

 what would occur at the mouth of a great river ; and the fluvio-marine tertiaries of 

 the Isle of Wight and Hampshire present a good example of the accumulation of 

 deposits in a tidal estuary, whose axis ran from east by south to west by north. 

 Many curious facts respecting the rise and fall of the tide and the currents due to 

 the action of the prevailing west winds are seen in the old red sandstone of the cen- 

 tral district of Scotland, and in the carboniferous strata of the north of England ; 

 and they present most determinate data for forming a conclusion with respect to the 

 distribution of the land and sea at those periods. The carboniferous strata show 

 that most remarkable changes must have occurred between their formation and that 

 of the magnesian limestone ; because the lines of rise and fall of the tide in those 

 two epochs in Yorkshire are nearly perpendicular to one another. Proceeding 

 upwards to the coal strata, to where tidal influence ceases, the author is of opinion 

 that the currents were chiefly due to the action of the wind ; for in the neighbour- 

 hood of Shefiield he finds that there is a most close agreement between their direc- 

 tions and that of the winds of the present period ; and that their general character 

 and arrangement agree better with this supposition than with any other that has 

 yet occurred to him. 



Stratified rocks of every period that have been thoroughly explored in this manner, 

 lead to the conclusion that their structure not only agrees with what would take 

 place from the action of the winds and tides, but furnish good evidence to prove 

 that no other agent could have produced them than such as are met with in modern 

 seas, and acting with no greater intensity than is now seen in various parts of the 

 globe. The application of this subject also furnishes many facts of considerable 

 interest in connexion with many other branches of theoretical geology. 



The author illustrated his subject by an appropriate assortment of maps, and an 

 ingenious machine representing the action of the waves. 



On a Phyllopod Crustacean in the Upper Ludlow Rock of Ludlow, 

 Discovered by R. Lightbody. By the Rev. W. S. Symonds, F.G.S. 



This fossil is the trifid tail of a crustacean apparently allied to Hymenocaris 

 vermicmida of the lower Silurians of North Wales, and was discovered by Mr. 



