Davis — Quarries in the Lava Beds at Meriden. 3 



district is shown to be divided into "blocks" or "slabs," by a 

 system of faults, here running obliquely with much regularity 

 about northeast-southwest. Each block, whether wide or nar- 

 row, contains representatives of the normal sequence of sedi- 

 mentary and igneous beds; the most important of the latter 

 being the " main trap sheet," — the greatest lava flow of the 

 region — which always stands up as a dominating topographic 

 element. The name locally given to the ridge formed in each 

 block by the main sheet is here extended to the block itself; 

 the initials of the name of each block standing over the 

 northern margin of the diagram.* The faults are numbered 



beneath the diagram ; two important faults occur southeast of 

 the area here included, and the count therefore begins at 

 " 3." All the faults here shown, except the last one, have the 

 upheaved side on the east, and hade steep to the downthrow, 

 as far as determined. Two examples of small uplift on the 

 west are known, one being number 11 and the other occurring 

 a little north of the district here portrayed. In addition to the 

 strong ridge of the heavy main sheet, there are in each block 

 two smaller ridges, one in front of the outcropping face of the 

 main ridge, the other behind its back slope ; and hence called 

 by Percival in his Survey of Connecticut some sixty years ago 

 the anterior and posterior ridges. As all these ridges are but 

 the topographic expressions of three extrusive lava sheets, the 

 terms anterior, main and posterior, may be used in a chrono- 

 logical as well as a topographical sense. Near the left front 

 margin of the diagram, the northern terminal members of the 

 West Rock and Gaylord mountain range are seen ; their whole 

 length being indicated on tig. 1, north of JSTew Haven. These 

 ridges are formed on an intrusive trap sheet, apparently tilted, 

 dislocated and denuded in the very manner that prevails with 



* The initials on the upper margin of figure 2 are as follows : B., Higby ; C, 

 Chauncey; L., Lamentation; Q., Quarry; C. H., Cat-Hole; N., Notch; W. P., 

 West Peak ; S., Short. 



