122 G. W. Hawes- RocJcs of the ''Chloritw formation:' 



spar — must have been a result of the metaraorphic process. 

 And its formation was probably favored by two conditions in 

 the original mud-beds so changed; (1) the presence of a com- 

 paratively small percentage of silica, or not over 50 per cent ; 

 and [2) the presence of much disseminated carbonate of lime 

 probably derived mainly from pulverized fossils. The fact that 

 the chloritic formation contains two or more beds of limestone 

 is reason for supposing that the mud elsewhere may have been 

 more or less calcareous. The oligoclase of the metamelaphyre 

 required for its formation only that the mud should contain a 

 little more silica and soda and less lime. 



The terms doleryfe and dmbase are here retained for the igne»ns 

 rocks which have been so called — diabase being applied to the 

 chloritic variety of doleryte.* Some German works on Lithol- 

 ogy restrict the term doleryte to dolerytes not older than the 

 Tertiary, and call the other kinds, whether chloritic or not, 

 diabase. But this is giving different names to the same corn- 

 pound ; and it is making geological age — a criterion fortunately 

 never considered in the naming of other rocks — override differ- 

 ence of mineral composition. 



Art. XlU. — ConiribW ions from the Sheffield Laboratory of Yak 

 Colkge. No. XXXVIL— 7V,e Rocks of Vie '•Chloritic formation'' 

 on the Western Border of the Xew Havm region ; by GeoeGE 

 W. Hawes. 



Woodbndge and Orange, 

 .and which have been described in the foregoing article by 

 Professor Dana, bear, as he states, a close resemblance to the 

 trap rocks of the Connecticut Valley. It hence becomes interest- 

 ing to ascertain whether the similarity is sustained by their 

 chemical composition and mineral constituents. 



As in the case of the trap, these rooks are of different 

 kinds. Firsts dark-colored crystalline rocks very similar in 

 color, texture, fracture, and specific gravity, to the undecom- 

 posed dolerytes of this region; and second, rocks which are 

 more or less green and appear to be chloritic, very closely resem- 

 bling the diabase. The latter kind has itsporphvritic varieties. 

 Besides these there is a third kind which contains a higher per- 

 centage of silica, and has the composition of melaphyre. 



I. Metadoleryt^. — A specimen collected from an outcrop about 

 a mile south of Maltby Park (on what was formerly Mr. 



valley -the 



chloritic condition of part of the ti 

 -tne part distinguished here as diabase — see this 



