4 Davis — Quarries in the Lava Beds at Meriden. 



the extrusive sheets ; but in the present paper the intrusive 

 sheet need not be further considered.* 



It is manifest from figure 2 that the true stratigraphic 

 sequence of the formation can be detected only by moving 

 obliquely to the strike within the boundaries of a single 

 " block ;" but this is by no means manifest on the ground, for 

 the fault lines by which the blocks are bounded cannot be seen 

 except in rare instances and for very short distances. Hence 

 it is important that the field evidence on which the existence 

 of the faults is based should be carefully argued. An essen- 

 tial postulate in this argument is the extrusive origin of the 

 three lava sheets, above mentioned : for extrusive sheets may, 

 in spite of their igneous origin, be treated as if they were 

 normal members of the stratified sedimentary series ; and of 

 all this series the lava sheets are of the greatest value in field 

 work, on account of their strong outcrops. It is therefore of 

 prime importance that the postulate as to the extrusive origin 

 of the sheets should be carefully tested. Both these points, — 

 extrusive origin of lava sheets, and existence of oblique faults, 

 may be well studied in the Meriden district ; and no single 

 locality offers so large a variety of features for examination as 

 the Quarry ridge in its present excellent condition of deep dis- 

 section. The district has become especially familiar to me on 



*Some of my earlier articles seem to have given the impression that T regarded 

 East Rock, New Haven, as belonging with the extrusive sheets of which Salton- 

 stall and Totoket mountains are typical examples, and not with the intrusive 

 sheets, of which West Rock and Gaylord's mountain are the type. Nothing has 

 been further from my intention. My first summer's work on the Trias, in 1882, 

 convinced me of the intrusive nature of East Rock, on the back slope of which 

 " a very strongly baked granitic sandstone is found within a few feet of fine com- 

 pact trap " (On the Relation of the Triassic Traps and Sandstones of the eastern 

 United States. Bulletin Museum Comp. Zool., vii, 1883, 268.) Salionstall ridge 

 was regarded at the same time as an extrusive sheet, and contrasted with the 

 intrusives, "such as East Rock and the Palisades" (ibid, 269). Specific account 

 of the evidence on which the intrusive nature of East Rock was argued is given 

 in the essay by Mr. Whittle and myself, entitled "The Intrusive and Extrusive 

 Triassic Trap Sheets of the Connecticut Valley " (Bulletin M. C. Z., xvii, 

 1889, 105). 



Another point in which my interpretations have been misunderstood concerns 

 Mt. Carmel and the associated large dikes of the Blue Hills, southwest of Wal- 

 lingford. I have been quoted as calling these dikes "buried volcanoes," but on 

 the other hand I have regarded them as the underground necks of volcanoes 

 from which some of the extrusive sheets were poured out. As such they are 

 monuments of " lost volcanoes," but they are by no means "buried volcanoes." 

 (See Bull. Geol. Soc. America, ii, 1891, 420-421; also, The Lost Volcanoes of 

 Connecticut, Pop. Sci. Monthly, Dec, 1891, 226.) Having sometimes been taken 

 to task for not considering the flows of Saltonstall, Totoket and the other ridges 

 farther north to be iutrusive sheets, it is now a little amusing to be called to 

 account for not considering the undoubtable intrusive sill of the Palisades in New 

 Jersey to be an extrusive sheet, and this on no other evidence than its great 

 extent roughly conformable with the bedding. (See Lyman's recent Report on the 

 "New Red" of Bucks and Montgomery Cos., Penna., in Einal Report, 1895, iii, 

 2621.) 



