ON THE GRANITE NKAK PLYMOUTH. 



37 



They are of a light-brown colour, somewhat long. The corselet very 

 thick, having internally two small, longish, dusky-brown bodies; there 

 is an erect conical tube on the outer margin of the eighth ring, and a 

 rugged tuft of hair under the tail. The adolescent insect (nymphe) 

 is- brown, generally curved; large before, having two horns, with two 

 round leaf-like fins at the vent. After eight days' repose, the full- 

 grown gnat comes forth. DE GEER'S WORK, as above quoted. 



ON THE GRANITE NEAR PLYMOUTH, AND THE INFERTILITY 

 OF GRANITE SOIL. 



BY JOHN PRIDEAUX, ESQ.* 



THE granite of Dartmoor, from Mistor to Heytor, and south of that 

 line, has the following characters ; which probably belong to the 

 whole. 



It is entirely mountainous, the highest hills being on the borders ; 

 where some of them attain an elevation of nearly two thousand feet. 

 The valleys run in various directions ; but have a tendency upon the 

 whole to the north and south line. The hills rise often steep, some- 

 times precipitous ; their sides scantily clothed with long grass, except 

 where rushes or moss indicate subjacent bog ; and often strewed with 

 loose blocks of granite, from fifty or more tons down to the size of a 

 flag-stone. A crag, called the tor, usually projects at the summit of 

 the hill, having a very striking appearance of stratification ; thejissures 

 being sometimes horizontal, more commonly a little inclined. This 



* From the Transactions of the Plymouth Institution, kindly sent us by Dr. E. 

 Moore. 



