A HISTORY OF CORNWALL The ' killas ' which separates the conglomerate of the Meneage district from the fossiliferous Devonian strata of the Newquay district, has been divided into three lithological divisions, viz. the Portscatho series, the Falmouth series and the Mylor series. 1 All these divisions are composed of argillaceous and sandy alternations, and all are characterized by the absence of limestone. Their lithological types are however suffi- ciently distinct to admit of their being separable on geological maps. The Portscatho and Mylor series are blue and dark in colour ; the Port- scatho contains the coarser sandstone beds, while the Mylor rocks besides being more shaly are more distinctly banded. The Falmouth series exhibits greater variation, is usually buff in colour, but includes zones which are purple and red. The rocks also appear to be of lesser thickness than either of the two series which they divide. Their occurrence in the Fal basin between Falmouth and Truro in a series of parallel lenticles is an ad- mirable illustration of the geological structure of the county ; for although the strata have a general south-easterly dip, and we are apparently cross- ing the strike from the coast to the heart of the county, yet instead of getting deeper in the stratigraphical series we are on precisely the same geological horizon at Truro as at Falmouth, the intervening ground being made up of a succession of isoclinal folds. On leaving the barren belt occupied by these rocks we find between Holywell Bay and Boscastle on the north coast, and between St. Austell Bay and the Tamar on the south coast, an assemblage of strata which is not only fossiliferous, but in which limestones occur. The fossil re- mains with which they are charged leave little doubt that this belt is occupied in the main by Devonian strata, but until the region has been more closely investigated it would be unsafe to assume that an area so folded is entirely restricted to that formation. It is possible that the fine grained conglomerate of Probus and Grampound and the Nare Point conglomerate may represent an unconformity dividing the Silurian and Devonian formations. As the northern coast of Cornwall truncates the Culm Measures as well as Devonian rocks, while the former are not seen on the south coast, a brief description of the fossiliferous rocks of north Cornwall will sufficiently indicate our knowledge of the palasontological remains that are entombed within the strata. For the following description of those formations we are indebted to Mr. Howard Fox : The rocks of the north coast of Cornwall do not yield fossils in as good a state of preservation as those of the south-east coast and of the South Petherwin beds near Launceston. Between Holywell Bay and Newquay no determinable fossil of interest has as yet been found. At Newquay Mr. Clement Reid has recently collected a considerable num- 1 J. B. Hill, Summary of Progress of the Geological Survey for 1898, p. 97. 38
