Jekyll Not Displaying Layout for Static Page

问题

in root folder I have

designing_minimalist.md

---
title: Case Study: Designing Minimalist Interfaces For Teaching New Cognitive Tool Use
layout: default
---

# Case Study: Designing Minimalist Interfaces For Teaching New Cognitive Tool Use

Quantum Pilot is a SHMUP-puzzle about fighting clone ships that mirror how you attack them. (...)

default layout:

<html>
<body style="background-color:black">
<body link="white">
<body vlink="white">
<style>
a {
    text-decoration: none;
}
</style>
<h1><a href="index.html">main</h1>
<div class="row-fluid">
    <div class="span8" style="color:white">
        {{ content }}
    </div>
</div>

When I run jekyll build, I get _site/designing_minimalist/index.html

but my root/index.html file has the default layout:

<html>
<body style="background-color:black">
<body link="white">
<body vlink="white">
<style>
a {
    text-decoration: none;
}
</style>
<h1><a href="index.html">main</h1>
<div class="row-fluid">
    <div class="span8" style="color:white">
        <p><a href="https://itunes.apple.com/us/app/quantum-pilot/id935956154?mt=8">>Quantum Pilot: Clone enemies remember how you killed them and fight back mirroring your attack</a></p>

<p><a href="designing_minimalist/index.html">>Case Study: Designing Minimalist Interfaces For Teaching New Cognitive Tool Use</a></p>

    </div>
</div>

root/index.md

---
title: main.
layout: default
---

[>Quantum Pilot: Clone enemies remember how you killed them and fight back mirroring your attack](https://itunes.apple.com/us/app/quantum-pilot/id935956154?mt=8)

[>Case Study: Designing Minimalist Interfaces For Teaching New Cognitive Tool Use](designing_minimalist/index.html)

Why is the default layout not being applied to my static page?