310 Mevieivs — TJte Geology of the Lizard. 



separated by a fault or thrust-plane, heading to the south and south-east, 

 and carrying well-marked breccia. The disturbance is well shown near 

 Polurrian Cove on the west and near Porthallow Cove on the east, but 

 it cannot be definitely traced throughout the intermediate ground. 



The southern area has been mapped and described by Dr. Flett, 

 the northern by Mr. Hill. The entire region is a somewhat irregular 

 plateau, averaging about 280 feet in elevation, but rising on the 

 serpentine of Goonhilly Down to 370 feet, and on the hornblende 

 schist of Koskruge Beacon, west of Porthallow, to 378 feet. This 

 plateau, eroded to a great extent probably in Miocene and early 

 Pliocene epochs, was further planed down in later Pliocene times, 

 when the area was submerged to the extent of about 420 feet. 

 Eelics of gravels regarded as of Pliocene age (but not fossiliferous) 

 occur on the gabbro of Crousa Common north of Coverack. 



The coastline in general is rugged and rocky, and often difficult 

 of access, but characterized by numerous highly picturesque coves, 

 while the broad tidal waters of the Helford Kiver and the Loe valley 

 south of Helston are bordered by wooded slopes of great beauty. 

 The region in general is described as essentially an agricultural and 

 not a mining country, and in this respect it compares with the 

 metamorphic area of Salcombe in South Devon, which is included in 

 the fertile district of the South Hams. In the Lizard the least 

 cultivated portions are on the serpentine, which yields a thin clayey 

 soil, liable to be waterlogged, and the land is comparatively barren 

 and dreary. 



A full, and in all respects excellent, accoimt of the previous 

 literature relating to the Lizard Series is given by Dr. Flett, and 

 it is interesting to read of the gradual progress of knowledge and 

 of the diverse views concerning the origin and relations of the rocks 

 in this complex area. To the elucidation of the problems Professor 

 Bonney, Dr. Teall, Mr. Howard Fox, Mr. Harford J. Lowe, also 

 the late General McMahon and Alexander Somervail, have been the 

 principal contributors. It has remained for Dr. Flett to examine 

 in detail the entire area and bring the experience gained by seeing 

 the whole of the evidence to the interpretation of the mineral changes 

 in the rocks, their sequence, and structural features ; and it may 

 be affirmed that as complete a story as possible has been unfolded 

 by the masterly way in which this petrographical area has been 

 investigated. The one point on which we fail to find definite 

 expression of opinion is that of the geological age of the Lizard rocks, 

 though it may be inferred that Professor Bonney's reference of the 

 mica schists to the Archaean is not contested by Dr. Flett, who 

 regards the Old Lizard Head Series as "an important part of the 

 Lizard schists".^ Moreover, the intimate connexion of the series 

 appears manifest when we read that "in 1893 Somervail advanced 

 the hypothesis that all the principal rocks of the district, the horn- 

 blende schist, serpentine, gabbro, black dykes, and banded gneisses, 

 were differentiated from one magma. As he had already arrived at 

 a correct conception of the sequence of these rocks, he may be regarded 



^ See also Flett's account of "The Geology of the Lizard" (Proc. Geol. 

 Assoc, xxiv, p. 118, 1913). 



