GEOLOGY OF TJIE CONNECTICUT VALLEY DISTRICT. 45 I 



blance suggests identity of age, though not proving it without a further stratigraphical 

 study of the region between. 



7. At Littleton, also, fifty miles south-south-east of Lake Memphremagog (S. 24° 

 E.), there is a limestone, half metamorphosed, containing Helderberg corals, — one of 

 the important discoveries of Prof. Hitchcock, to whom I am indebted for guidance 

 over the region. The limestone is associated with quartzite and clay slate, and also 

 with a series of chloritic rocks, partly feldspathic, including chloritic slate and a kind 

 of protogene, in which a pseudophite-like mineral is disseminated in small grains ; and 

 it appeared to me that all were conformable. If this conformability is sustained by 

 further observations, we shall have here the additional lithological fact that chlorite 

 rocks, including protogene, may constitute metamorphic beds of Helderberg age. 



8. The facts which have been presented sustain the statements made on an early page 

 of this article, that lithological evidence of geological age is to be distrusted. If, when 

 used by one who has made it a special study, it leads to the conclusion that true 

 Helderberg xozVs in the White Mountain series are of Cambrian or earlier age, it is 

 surely a bad reliance. If it also makes out that Green Mountain rocks are of Huron- 

 ian age, or of some pre-Silurian period, when in reality belonging to the later part of 

 the Lower Stliiriatt, geologists may well be afraid even of its suggestions, unless it 

 have sure stratigraphical support. " Huronian" areas have been defined in various 

 parts of the country and the world on the basis of this evidence alone ; and in such 

 cases who knows anything whatever with regard to the real age of their rocks ? It is 

 probable that the rocks considered characteristic of the Huronian occur also among 

 true Laurentian terranes ; it is certain that they do in formations later than the Lower 

 Silurian. 



Finally, what reason is there in chemistry or geology why crystals of andalusite and 

 staurolile should have been made only in pre-Silurian times? Andalusite consists 

 simply of silica and alumina, and staurolite of the same, along with iron. These three 

 ingredients are now and ever have been the most abundant of all the mineral constitu- 

 ents of the globe. With or without the iron, they are the materials of all clay depos- 

 its ; and clay deposits, from the decomposition of granite, gneiss, and related rocks, 

 have been forming all over the globe, and increasing in amount, ever since these rocks 

 began their existence. They are therefore the very last minerals that should be thought 

 of as pre-Silurian "fossils." Were zirconium, or any other of the rare metals a con- 

 stituent in the species, there would be some reason for suspecting their restriction to 

 the more ancient formations, since later sediments would contain only traces of them. 

 But silica, alumina, and iron belong to all time. These remarks apply equally to chlo- 

 rite, in which these three ingredients occur, with only a litde magnesia besides, and 

 water. 



9. The epoch of disturbance, in which these Helderberg rocks of the Connecticut 

 valley were upturned and crystallized, was probably that closing the Devonian, when, 

 as Dawson and others have shown, extensive upturning, plication, and crystallization 

 of Devonian and older rocks took place over New Brunswick and Nova Scotia. It was 



