264 J. Bar r ell — Relations of Subjacent Igneous 



and in the included metasediments, and as such zones has 

 been described by Emerson as the Lee gneiss. He 

 considers that both differentiation and some solution of 

 sediments have occurred, but rather broad areas of these 

 rocks are found without visible relations to contact rocks. 

 The relations, however, all permit these amphibolitic 

 ribbon gneisses to be looked upon as roof rocks to the 

 Laurentian batholith. They belong in general to an early 

 stage, they average more basic, corresponding to the 

 marginal basic facies so common in batholiths, and they 

 show intermittent injection. The presence of much 

 water-vapor is the natural explanation of many of the 

 associated features. 



Cutting the foliated and granulated biotite gneisses 

 and amphibolites are younger bodies of massive granite 

 which range from biotite granites to aplites and pegma- 

 tites. Dikes of these are well displayed in the railroad 

 cut at West Norfolk, Connecticut. These intrusions are 

 later than the regional metamorphism. It is possible that 

 they might be much later, but their associations in the 

 Becket areas, their acidic character, and the analogy 

 with the other localities to be described suggest that they 

 are more probably parts of the same igneous cycle, that 

 the regional metamorphism proceeded during the same 

 period, but had spent its force before the last intrusion of 

 granites. 



The Paleozoic batholiths of Connecticut are much more 

 satisfactory for study, since their structural relations 

 with their roofs are widely revealed."^^ The outcrops of 

 the batholiths are elongate or rounded forms. Around 

 the margins many show a basic border rich in hornblende 

 and biotite. As in the Becket gneiss, the basic border 

 shows a highly variable and banded character. A very 

 considerable degree of mashing is to be observed, as 

 shown by the degree of crumpiling of the oldest icross- 

 cutting pegmatites. The oldest gneisses are biotite 

 granite in composition, and the gneissic structure is well 

 developed. The basic border is a differentiation phase 

 of these, as shown by the uniformity with which it 

 constitutes the margin and intrudes the surrounding 

 sediments. The pegmatites in this zone are of two ages, 



^^ For detailed descriptions of the Conneeticut formations, see W. N. Eice 

 and H. E. Gregory, Manual of the geology of Connecticut, Conn. Geol. Nat. 

 Hist. Survey, Bull. 6, 1906. Also T. N. Dale and H. E. Gregory, The gran- 

 ites of Connecticut, U. S. Geol. Survev, Bull. 484, 1911. 



