A series of Questions for our Geologists.

'A shape', no, but if we see many such shapes it indicates a system. The question becomes whether that system is natural or not. Under the proper conditions, virtually all materials can flow. But then, they MUST be designed... That is the whole point, isn't it? Why are supernatural explanations so compelling to some people when they are totally unnecessary?

I'm trying to say that I agree with you.

You are correct. These are folded sedimentary rocks related to the Appalachian orogeny. The same thing occurs near my old alma mater in the Valley and Ridge physiographic province - not sure what they call it down there. The lineations are formed by folding and thrust faulting of the early Paleozoic sequence consisting of varying lithologies. Variable erosion has led to definition of the surface features including long, linear ridges and intervening valleys. They are cut off on the southwest end by the embayment that Rox talked about. This is pretty basic geology where the older Appalachian structures are cut by the younger unconformity (which of course doesn't really exist according to YECs) upon which the Mesozoic rocks have been deposited. The last major event is regression of the sea which leaves the younger rocks exposed. The arc you described earlier is an unconformity.

If you want an idea how the lines formed just look at the area NW of PHiladelphia from about 200 miles. it shows fairly well, the geometry of the folds.

I am not going to spend much time with this. We can tell the kinematics of the event by the vergence of folding. We can also see the uplifted parts of the crust in the cores of the mountain ranges. We can also see the metamorphic assemblages that suggest deep burial, but they are now at the surface. As Ned notes, we can also see sedimentary patterns and unconformities that suggest uplift above base level. If there is another explanation for these and other data, I'd love to hear it.

In general, the assymetry of the folding shows movement from the east toward the west. This conforms to the direction of thrusting that we see in the same rocks. That means that the eastern margin of the NA continent was likely overriden by crustal rocks from the east, in this case the African continent. Fortunately, we have fragments of this overriding continent in the Blue Ridge and its equivalent crystalline rocks.Crystalline rocks of the Precambrian form the basement rocks for the Paleozoic rocks. These are exposed in places like the White Mountains and other areas, possibly as referred to by other posters. The fact that these rocks are exposed at the surface and the sedimentary rocks uplifted around thme suggests that there was a mountain range.The metamorphic minerals are part of the crystalline complex, but also occur in the sedimentary sequence. This means that they have been buried much deeper than they are today. The assemblages are also zoned so that we can generally see more deeply into the mountain range by using the higher temperature minerals. In fact, as a curiosity, there is a mineral assemblage known as blueschists in parts of the greater Appalachian orogney that suggest deep burial but low temperatures. This is consistent with being rapidly overidden by a large, package of supracrustal rocks. And no, I wouldn't expect your layman to recognize the metamorphic assemblages without some
help.Because of differential erosion of multiple orogenic events, the picture of the entire orogen can be quite complex even though a single area can be explained rather easily. The linear ridges you see throughout the Valley and Ridge Province is the effect of eroding upturned sedimentary rocks that have been folded along hinges that run roughly parallel to the continental margin. The reason the seem to swirl around is that the folds do not have horizontal hinges. In other words, the folds have swales and culminations that stand lower and higher than other parts of the folds. That is why we see all of the Z patterns in the northern part of the province.

Coragyps,Good link. In fact, it mentions blueschists in the Arbuckle Mountains. The only problem is that the guide is wrong. They are high-pressure and low-temperature indicators, not the other way around. I'm certain it's just a typo.Nevertheless, this guide shows a feature that can only be described as the core of an old mountain range that has been deeply eroded. It is an uplift with the oldest rocks in the center and younger rocks as you traverse outward from the core. This is the classical way of identifying anticlines (fold crests) as opposed to synclines (the fold troughs).

Don't see it. Try lat/long.

Ah. It's an erosional feature at the edge of the Appalachian Plateau. It looks like a small plateau or mesa made up of the flay-lying Pottsville Formation. YOu can see the flat layering in the Google-Earth depiction. This is a common feature to the north and west of the Appalachian orogen. Deformation dies out west of the mountains and we get flat stratigraphy dissected by dendritic patterned drainages rather than the trellis pattern of the Valley and Ridge province. See if you can find your way through to the geological map of Alabama from this site:GSA/OGB

Erosion of flat-lying sediments. The topography reflects the layering. Probably of a resistant bed. Happens all the time. Well, it had to be raised above sea level first, but basically, it is an erosional feature.You are welcome...This message has been edited by edge, 02-05-2006 11:53 PM

The latter. But if you look to the NW, the plateau continues in that direction. Without the effects of erosion it would be part of that same plateau.

That's what I thought at first, but the top of the hill is flat and there appear to be flat-lying features visible even in Googlearth. This was perplexing, until I found the interactive geologic map of Alabama. It states that the feature is part of the Allegheny Plateau province which is characterized by flat beds. The Valley and Ridge province, where I thought we were, is mostly to the south and east of this area. Yeah, there are plenty of those in the area that I mentioned to Jar in central PA. Used to drive through there all the time and actually did some mapping in the area. That's why I referred to it earlier. It shows pretty clearly the V&R topography.By the way I spent some time with the dregs last night.

Yeah, well, I used to live there ... unfair advantage. I even did a research paper on the relationship between Blue Ridge and V&R provinces. And then the transition to plateau is pretty distinct, farther north.This message has been edited by AdminJar, 02-08-2006 08:12 PM