196 Rev. W. D. Conybeare on the Phenomena of Geology. 



nomena they undertake to explain : for instance, of the struc- 

 ture of Luneburg Heath, and all the vast diluvial flats of the 

 North of Germany. These are occupied by one vast accumu- 

 lation of gravel, partly chalk flints, derived, probably, from a 

 zone of that formation, which must originally have occupied 

 this tract (as may be seen from the chalk-pit at Luneburg), 

 but every apparent mass of which has been swept away, and 

 buried beneath its own ruins: but with these are intermingled 

 vast blocks of granite, often as large as small cottages, for 

 which, at a little distance, I have more than once mistaken 

 them; this granite being derived from the Norwegian moun- 

 tains, on the opposite side of the Baltic. Now I will attempt 

 to explain all this on the Fluvial theory. First, the rivers now 

 flowing through the North of Germany must have changed 

 their course so frequently, as to have covered, successively, 

 every inch of the North of Germany, since this gravel is uni- 

 versally distributed : and this they must have done, though we 

 do not find from the earliest records preserved of the topo- 

 graphy of the country, that they are in the habit of changing 

 their course in the least. Secondly, they must have washed 

 away every projecting mass of the chalk formation, although 

 we do not find that the slightest mound of the most ancient 

 entrenchments in the neighbourhood has been sensibly affected 

 by atmospheric causes for some thousand years. Thirdly, 

 they must have carried blocks of many tons in weight for 

 some hundred miles, though they have now unaccountably 

 left off transporting any thing of more than a few ounces, and 

 that only for short distances. Fourthly, they must have trans- 

 ported these blocks up their currents ; since the granite is de- 

 rived from the opposite side of the Baltic, but the actual 

 course of all the streams is towards the Baltic. I have always 

 admired the seemingly sarcastic ingenuity of the ancient geo- 

 metricians, in adopting the reductio ad absurdum as a mode 

 of demonstration ; but I doubt whether even the fertile ima- 

 gination of these worthy elders ever conceived any thing quite 

 equal to this. 



But I will come nearer home. The great plain of London 

 is deeply and universally covered with flint gravel, apparently 

 derived from the chalk ridges of Hertfordshire, &c. : in that 

 plain arise many insulated hills, as Highgate, Harrow, &c., and 

 these hills are equally capped with flint gravel. Now, as no 

 stream (not even Father Thames) can roll gravel up hill, we 

 must suppose that the original surface of the plain was once 

 at the same level as the tops of these hills, in order to allow the 

 chalk flints to have been transported thither : and while things 

 were in this state, we must suppose the then Thames to have 



changed 



