XVII. On the Transport of Erratic Blocks. By William Hopkins, M.A. 

 and F.R.S., Fellow of the Cambridge Philosophical Society, of the Royal 

 Astronomical Society, and of the Geological Society. 



[Read April 29, 1844.] 



The instability of opinion which usually, and perhaps necessarily, characterizes the earlier 

 researches into any new and extended branch of philosophical enquiry, is strongly exemplified 

 in the different views which have been entertained respecting the causes to which the transport 

 of erratic blocks is to be referred. In the first stages of the enquiry rapid currents of water 

 were generally recognized as the most probable agents in these phenomena. No attempt, however, 

 was made to calculate the power of this agency, and the theory was associated with hypotheses 

 far too extravagant to bear the test of careful investigation. The natural consequence was the 

 very general abandonment of the theory on the suggestion of another possible cause of the 

 phenomena in question. It was represented that floating ice might have acted as vehicles of 

 transport, and many facts were collected, from the reports of those who had visited the colder 

 latitudes, confirmative of this opinion. Again, this latter theory has been lately endangered by 

 the recognition, on the part of some geologists, of a third theory, which attributes the transport 

 of blocks to the sole action of glaciers ; a view of the subject which has arisen out of the curious 

 and interesting observations recently made on the movements of existing glaciers, and the phe- 

 nomena indicating their far greater extension at some preceding geological epoch. 



The entire rejection of any one of these theories would imply a forgetfulness of the fact, 

 that geology is, in a peculiar sense, a mixed science, not merely as involving investigations which 

 properly belong to widely different branches of physical and natural science, but also as treating 

 in some instances of phenomena, (as in the cases of erratic blocks of different kinds, or in different 

 localities,) which, while they possess a great community of character, may be referrible to totally 

 dissimilar causes. Both glaciers and floating ice are manifestly adequate with respect to their motive 

 powers, to produce the phenomena in question. In the following communication I shall investigate the 

 transporting powers of currents of water, and shall shew that, under certain conditions, such currents 

 would be generated of sufficient velocity for the transport of boulders, and consequently that this 

 cause is also adequate to produce the removal of at least a large portion of the boulders which have 

 travelled from their original sites ; and that, therefore, the theory is not to be rejected on account 

 of any apparent inefficiency in the cause of transport assigned by it, or the extravagances which 

 have been formerly associated with it. AVe shall thus, I conceive, be constrained to recognize the 

 general adequacy of each of the three causes of transport above mentioned ; and in the further 

 examination of the problem it will only remain for the geologist to ascertain, as far as possible, the 

 share which each cause has had in producing the actual phenomena of transport by a careful 

 comparison of observed facts with the probable results of each mode of transport. Each group 

 of erratic blocks, or each mass of transported materials, may present in this respect a separate 

 problem ; in the present communication I shall only offer on this branch of the subject a few 

 general observations, without entering into any discussion of particular examples, beyond what may 

 be necessary for the elucidation of general views. 



