112 



Scientific Geology. 



employed, as it is by most geological writers, to include the loose ma- 

 terials and soils embraced in the alluvial, diluvial, and tertiary forma- 

 tions, as well as those solid masses, to which the term is limited in its 

 popular sense. 



It is well known that there is not a little diversity among the ablest 

 writers in respect to the names of rocks. Under such circumstances 

 an infallible nomenclature is out ofthe question. But if, as I intend 

 to do, I describe definitely what is included under each name attached 

 to the accompanying geological map, it seems to me that the difficulty 

 will be in a great measure obviated: especially as I shall present 

 specimens to the Government, of every variety of rock that is descri- 

 bed. And should they take measures for preserving this collection, 

 future geologists, may know precisely what is comprehended under 

 each rock mentioned in this report. 



Geologists are not agreed whether it is best to describe rocks in a 

 descending or an ascending order ; that is, whether they shall com- 

 mence at the surface with the most recent rocks, or with the lowest 

 hitherto discovered. Each plan has some advantages and some dis- 

 advantages peculiar to itself. Without stopping to assign the partic- 

 ular reasons, I shall choose a descending order ; that is, I shall 

 commence with the uppermost stratum, viz. Alluvium: and in adop- 

 ting this course, I follow the example of several of the ablest geolog- 

 ical writers of the day, such as Brongniart and De la Beche. 



As to the Classification of Rocks, there is also very much di- 

 versity among the ablest writers ; although there has been great im- 

 provement in this respect within the last 15 or 20 years. Yet excep- 

 ting a few general principles, the different systems for the arrange- 

 ment of rocks must be regarded as provisional merely, awaiting the 

 revision of some future Linnseus in geology. Among the principles 

 which I regard as established in the science, one is the division of 

 rocks into stratified and unstratifled. This division, therefore, I shall 

 adopt. But instead of stopping here to explain the subdivisions of 

 these classes, I shall introduce a Tabular View of the Rocks in Mas- 

 sachusetts, arranged as nearly as possible in the order of their super- 

 position ; and opposite their names, I shall put down the most impor- 

 tant and ingenious systems of arrangmentnowinuseamong'geologists; 

 so that a comparative view of them may at once be obtained. (See the 

 accompanying Atlas.) The first column contains the names ofthe 

 rocks under which I describe them ; the second column, the varieties of 

 each rock observed in Massachusetts : the third column, a catalogue 



