Notices and Extracts from the Minutes of the Geological Society. 139 



very materially from the rest of the mass in its agricultural character, being de- 

 cidedly unfavourable to vegetation; it has obtained the provincial appellation 

 of ravin. I have had frequent opportunities of verifying the accuracy of the 

 remark, both from direct experiments, and from observations on the growth 

 of plants, the roots of which had penetrated into this substance. The imme- 

 diate cause of its injurious effects would appear, in part at least, to depend 

 upon the tendency which it has to become indurated in dry and warm weather : 

 under such circumstances it has been rendered so hard as to be incapable of 

 being penetrated by a spade. 



The existence of this upper stratum would seem to indicate, either that the 

 whole of the clay was originally deposited in the way in which it now lies 

 with respect to its upper surface, or that, after the great body of the clay had 

 been deposited, and had experienced the action of various causes upon its sur- 

 face, the "ravin" was deposited by a subsequent and independent operation. 



The specimens now laid before the Society, were taken from the clay- 

 bank mentioned above, and may afford an idea of the nature and variety of 

 the rocks of which the pebbles are composed. It would not be easy to state 

 the proportion which the pebbles bear to the clay in which they are imbedded ; 

 but they are so numerous, that, in the more sandy parts, a square yard of the 

 clay would yield some dozens of them of sufficient size to be easily collected. 

 In all cases, or at least with a very few exceptions, they exhibit marks of 

 having undergone a great degree of attrition, their edges and angles being 

 very much worn down. With respect to the proportion in which the diffe- 

 rent kinds of pebbles exist, perhaps the most frequent are clay-slate, green- 

 stone, and basalt; the granitic are not uncommon, and some of the largest 

 masses consist of this rock : quartz pebbles are also not unfrequent, but 

 generally of small size. No decided organic remains have been observed in 

 this clay ; for although vegetable matter, and even what appears to be roots 

 of plants, is occasionally found in it, these may have belonged to trees that 

 have grown in the clay after it was deposited in its present situation. It is 

 worthy of remark, that when the clay is exposed to the atmosphere, it fre- 

 quently becomes clothed with a plentiful crop of the Tussilago Forfara ; and 

 this has been observed to be the case with portions of it that have been origi- 

 nally many feet below the surface of the earth. 



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