GEOLOGY OF MOUNT DESERT. 51 



fusion of included fragments broken from the country rock, 

 and a great branch-work of lateral granitic dikes penetrat- 

 ing the sides of the vast fissure. We shall later return to 

 consider the denudation of the ancient mass into its pres- 

 ent form ; but before that several facts of even more ancient 

 date than the granite intrusion must be examined. 



THE PRE-GRANITIC ROCKS. 



Even the casual observer can hardly fail to detect a 

 marked variety in the nature of the rock fragments 

 included in the granite along the southern and western 

 coast. Every one of these rocks is older than the granite. 

 Many of them are distinctly unlike in composition and tex- 

 ture, and probably also in age. Some are therefore older 

 than the granite by longer ages than the others. Their 

 sequence must be deciphered as far as possible.* 



The most manifest varieties of these older rocks may be 

 briefly described. On the western and northwestern coast, 

 and on some of the adjacent islands, as Bartlett and Hard- 

 wood Islands, there is an area of wrinkled greenish schists, 

 in somewhat disorderly attitude, associated with quartzitic 

 layers. Their southernmost occurrence is at Dix Point, 

 and northernmost at Thomas Island. The schists trend 

 northwest, north, and northeast, dipping to the eastward, 

 or towards the granite, at various angles. Their thickness 

 is estimated as two thousand feet at least These schists 

 are cut by the granite at several points, and hence belong 

 in the pre-granitic series ; but as they are not found in con- 

 tact with the other marginal rocks, it is only on account of 

 their gnarled and ancient appearance that they are placed 

 at the foundation of the history of the Island. They seem 



* A number of statements in this section, and in the section on the 

 glacial invasion, are taken from an essay by Prof. N. S. Shaler, on the Ge- 

 ology of the Island of Mount Desert, in the Eighth Annual Report of the 

 Director of the U. S. Geological Survey, Washington, 1889. 



