[ £84 ] 



Lir. Sketch of the Geologij of Madeira. By the Hon. 

 Henrv Grey Bennett ; in a Letter addre'ned to G. B. 

 Grkenough, President of the Geological Society, and 

 comvmnicaled by him to the Society*. 



JL HE following notes w ere taken during a short stay I made 

 last summer in the island of Madeira. As there appears to 

 be but liule known of the strueture, or otthe phoenon)ena 

 whieh the strata in that island exhibit, the t'ollowing ob- 

 servations may not perhaps be wholly unacceptable. They 

 may be considered as I'urnishing directions to others, where 

 to look for some of the most interesting objects; and may 

 afford to future travellers a small portion of llie information 

 which my guide. Dr. Shuler, so liberally communicated to 

 me. That gentleman having long resided in tiie island, had 

 repeatedly traversed it, and was thereby able to point out to 

 me some of the circumstances which were most worthy of 

 examination, particularlv the nature of the various strata 

 that are exposed to view m the deep and abrupt valleys which 

 intersect the island in all dnections. These valleys are no 

 Jess picturesque to the eye of the common traveller than 

 they arc deserving of the attention of the geologist. They 

 are in genera! narrow and deep, the summits of the hills that 

 form their boundaries are broken into peaks rugged and 

 bare, while their sides are covered with the cedar and other 

 trees peculiar to southern latitudes, and with a profuse va- 

 riety of shrubs and plants, among which the erica arborea is 

 the most beautiful, and in the greatest quantity. 



The island of Madeira (though I believe it never has been 

 surveyed) is said to be about 30 miles in length, and in its 

 broadest part about 20, but the average breadth dues not 

 exceed 15 nulcs. 



it con-'isis of a succession of lofty hills rising rapidly 

 from the sea, particidarly on the eastern and northern ex- 

 tremities. The summits of many of these ranges present 

 the appearance of what has been called a table laiul; yet oc- 

 casionally the forms are conical, and SMrmounied by a peak, 

 which HI some instances I found to be of columnar basalt. 

 Deep ravines or valleys descend i'rom the hills or serras to 

 the sea, and in the hollow of most of them iiows a small 

 river, which in general is rapid and shallow. The soil of 

 the island is clay on the surface, and larsie masses of it as 

 hard as brick are found underneath. Though there are not 

 at present any o.isting volcanoes in the island, yet the re- 

 mains of two craters are to be seen, one on the eastern, the 



* From Transactions of the Geological Society, vol. i. 



other 



