Paradoxically disappointing. This is an excellent geology of the area; it just isn’t a very good roadside geology. I sympathize somewhat; author James Skehan has the same problem that occurs in other eastern states; the highways are so congested that it is downright dangerous to stop or even slow down to look at outcrops. However, other books in the Roadside Geology series got around this by directing you to parks or other areas where you could examine things; Skehan does that to a certain extent but it isn’t integrated into the “roadside” format. Although the book Is organized by highway like the others, there are no road logs with mileage; instead it’s as if Skehan describes the geology of an area and only mentions the roads that lead through it in the chapter title and the maps.


Skehan also makes an annoying paleontological error – especial for somebody who has a trilobite genus named after him – he consistently describes hyolithids as molluscs, and implies they went extinct in the Cambrian. Their phylogenetic position is uncertain and although they have maximum diversity in the Cambrian they last until the Permian. (Added later: they’re now thought to be brachiopods, or at least lophophorates).

And as a final criticism, Skehan is a little too technical for the usual Roadside Geology audience. For example he uses the term “roof pendant” without defining it, comments that the calcium content of a rock shows it was formed in a subduction zone without explaining why, and uses “olistostrome” and “olistolith” without definition in text (although “olistolith” is in the Glossary).


All that being said, the area has really complicated geology. New England was subject to at least ten continent or island arc collisions or rifting events:


* Middle Proterozic, Laurentia and Amazonia collide as part of the assembly of Rodinia; Grenville Orogeny.

* Late Proterozoic, Rodinia rifts to make Laurentia, Baltica and Gondwanaland.

* Late Proterozic, Avalona island arc/microcontinent/terrane rifts off Gondwanaland; Avalonian Orogeny; Iapetus Ocean.

* Late Ordovician, Sherburne and/or Bronson Hill island arcs/terranes collide with Gondwanaland; Taconic Orogeny.

* Devonian, Avalon, Meguma, Putnam-Nashoba, Central Maine, Merrimack and maybe Gander microcontinents/island arcs/terranes collide with Laurentia, Acadian Orogeny. (The Gander Terrane isn’t exposed anywhere on the surface in Connecticut or Rhode Island but is likely underneath somewhere).

* Permian, last bits of Pangea come together, Alleghenian Orogeny.

* Jurassic, Pangea rifts, Atlantic Ocean. A parallel rift zone starts in the Connecticut River valley but the one a little further east takes over to make the Atlantic; this, the Rio Grande Rift, and the poorly exposed and understood Mid-Continent Rift are three examples of “failed rifts” in North America.


The major continental collision orogenies – Grenville and Alleghanian – probably created mountain ranges as big as the Alps or Himalayas. The terrane collisions would have created volcanic chains and mountains like the Cascades. Then all this stuff got planed off to more or less sea level (the highest point in Connecticut is 2379 feet, or about half the altitude of my basement floor; and it’s on the state line on the slope of a hill in Massachusetts).


It’s no wonder, then, that the state’s geology is a little difficult to figure out. This gives me more sympathy for the 19th and early 20th century North American geologists who dismissed continental drift; the Ivy League university geology departments didn’t see the relatively simple geology that the Southern Hemisphere had. (There was one mystery that might have convinced them, or at least made them think about it some more; the Cambrian trilobite genus Paradoxides was native to Avalonia. Thus it’s found in the bits and pieces of the Avalon Terrane that were scattered through New England and Europe when Avalonia rifted apart, but not in now adjacent Cambrian sedimentary rocks on either side of the Atlantic that were never part of Avalonia. Without plate tectonics, paleontologists attributed this distribution to quirky ocean currents and arm-waving, and gave the genus name to indicate the problem).


A few things that were surprises: Long Island Sound was once a freshwater glacial lake, Glacial Lake Connecticut; Connecticut was once the major iron producing colony in North America, starting in the 1730s. The iron came from limonite found on the contact between the Stockbridge Marble and the Walloomsac Schist.


Good photographs of outcrops; excellent maps and explanatory diagrams; an adequate glossary and a good bibliography; as mentioned the major failure is you can’t actually use it on roads in Connecticut and Rhode Island. This area might have been better treated as a part of the Geology Underfoot series. ( )